Add composer test entry point with phpcs

Import composer test and phpcs from mediawiki/extensions/BoilerPlate

Fix up a few phpcs issues:

Set indentations to spaces.
Add .editorconfig with indentation set to 4 spaces.

Short array syntax must be used to define arrays
(Generic.Arrays.DisallowLongArraySyntax.Found)
Control structure "foreach" must be followed by a single space
(MediaWiki.WhiteSpace.SpaceAfterControlStructure.Incorrect)

Add missing documentation to a few parameters addressing:
Doc comment for parameter "$x" missing
MediaWiki.Commenting.FunctionComment.MissingParamTag

Add a few whitespaces.

Use inline ignore comments for a couple place for which I did not want
to make any code change:

• Assignment expression not allowed within "while".
• Use static closure

Ignore most other rules.