Prettier v2 has the following breaking changes:
* enforces spaces between `function` and params
* enforces trailing commas by default

This is needed in order to use `globalThis`, see #1894.
It also made it possible to remove some old polyfills and fallbacks.

Handlebars v5 will target modern browsers,
while older browsers will still receive support
via version 4.x.

Fixes #1820
Closes #1821

By adding the `.js`-extension to the bin-file, IDEs will
know that js code-highlighting should be applied to the
file, which makes it easier for devs to read the code.

Also reorganized npm scripts.

This was found by running an IntellijIDE
code inspection for proofreading.

# Conflicts:
#	components/bower.json
#	components/handlebars.js.nuspec
#	components/package.json
#	integration-testing/multi-nodejs-test/test.sh
#	package-lock.json
#	package.json

Extracts the parser to `@handlebars/parser`, where it can be shared
between different implementations. This means that e.g. Glimmer/Ember
will be able to iterate on new features without forcing Handlebars to
adopt them immediately, and vice versa. All implementors will be able to
absorb changes as it makes sense for them.

# Conflicts:
#	integration-testing/multi-nodejs-test/test.sh
#	spec/string-params.js
#	spec/subexpressions.js
#	spec/track-ids.js

#1683)

This reverts commit c2f1e62.

- Add spec/tmp directory with .gitkeep file to indicate the folder is intentional
- Add the folder contents to .gitignore
- Use this folder to output the sourcemap file during bin tests. This file is a sideeffect of the main test

- adds full unit tests for all cli options
- demonstrates that nothing changes between minimist and yargs except a minor order change in the --help text
- proves b9c4b25 works the same as before

Co-authored-by: fabb <fabb@users.noreply.github.com>

# Conflicts:
#	components/bower.json
#	components/handlebars.js.nuspec
#	components/package.json
#	package.json

- helpers should always be a function, but in #1639 one seems to
  be undefined. This was not a problem before 4.6 because helpers
  weren't wrapped then.
  Now, we must take care only to wrap helpers (when adding
  the "lookupProperty" function to the options), if they
  are really functions.

This commmit adds the runtime options
- `allowProtoPropertiesByDefault` (boolean, default: false) and
- `allowProtoMethodsByDefault` (boolean, default: false)`
which can be used to allow access to prototype properties and
functions in general.

Specific properties and methods can still be disabled from access
via `allowedProtoProperties` and `allowedProtoMethods` by
setting the corresponding values to false.

The methods `constructor`, `__defineGetter__`, `__defineSetter__`, `__lookupGetter__`
and the property `__proto__` will be disabled, even if the allow...ByDefault-options
are set to true. In order to allow access to those properties and methods, they have
to be explicitly set to true in the 'allowedProto...'-options.

A warning is logged when the a proto-access it attempted and denied
by default (i.e. if no option is set by the user to make the access
decision explicit)

# Conflicts:
#	components/bower.json
#	components/handlebars.js.nuspec
#	components/package.json
#	package.json

Disallow access to prototype properties and methods by default.
Access to properties is always checked via
`Object.prototype.hasOwnProperty.call(parent, propertyName)`.

New runtime options:
- **allowedProtoMethods**: a string-to-boolean map of property-names that are allowed if they are methods of the parent object.
- **allowedProtoProperties**: a string-to-boolean map of property-names that are allowed if they are properties but not methods of the parent object.

```js
const template = handlebars.compile('{{aString.trim}}')
const result = template({ aString: '  abc  ' })
// result is empty, because trim is defined at String prototype
```

```js
const template = handlebars.compile('{{aString.trim}}')
const result = template({ aString: '  abc  ' }, {
  allowedProtoMethods: {
    trim: true
  }
})
// result = 'abc'
```

Implementation details: The method now "container.lookupProperty"
handles the prototype-checks and the white-lists. It is used in
- JavaScriptCompiler#nameLookup
- The "lookup"-helper (passed to all helpers as "options.lookupProperty")
- The "lookup" function at the container, which is used for recursive lookups in "compat" mode

Compatibility:
- **Old precompiled templates work with new runtimes**: The "options.lookupPropery"-function is passed to the helper by a wrapper, not by the compiled templated.
- **New templates work with old runtimes**: The template contains a function that is used as fallback if the "lookupProperty"-function cannot be found at the container. However, the runtime-options "allowedProtoProperties" and "allowedProtoMethods" only work with the newest runtime.

BREAKING CHANGE:
- access to prototype properties is forbidden completely by default

# Conflicts:
#	Gruntfile.js
#	package-lock.json
#	package.json

# Conflicts:
#	Gruntfile.js
#	package-lock.json
#	package.json
#	spec/amd-runtime.html
#	spec/amd.html

- add prettier to do formatting
- add eslint-config-prettier to
  disable rules conflicting with prettier
- remove eslint from grunt workflow
- use lint-stage to lint and format
  on precommit
- use eslint and prettier in travis directly
- remove rules that are already part of
  the "recommended" ruleset

That rational is that eslint and prettier should be run in
Travis-CI, on commit and as IDE integration (highlighting
errors directlry). They don't need to be run along with
test-cases. Getting linting errors when running the tests
because of missing semicolons is just annoying, but doesn't
help the overall code-quality.

Reintroduce "merge" function, no called "mergeIfNeeded", that only creates a new partials
object if both "env.partials" and "options.partials" are set.

closes #1598