Account for upstream changes related to PHP 7.4 arrow functions

[jrfnl]

See upstream issue: squizlabs/PHP_CodeSniffer#2523

Relevant commits which need to be emulated & made backward compatible (in as far possible):

• squizlabs/PHP_CodeSniffer@b74e813 (File::getMethodParameters() + associated tests)
• squizlabs/PHP_CodeSniffer@c8fca56 (File::getMethodProperties() + associated tests)
• squizlabs/PHP_CodeSniffer@37dda44 (File::getDeclarationName() + new tests needed)
• squizlabs/PHP_CodeSniffer@96e69bb (File::isReference() + associated tests)
• squizlabs/PHP_CodeSniffer@bbd6f63 (File::getMethodProperties())
• squizlabs/PHP_CodeSniffer@bf642b2 (File::findEndOfStatement() + associated tests)

The upstream changes are expected to be released in PHPCS 3.5.3.

Upstream will probably also contain a $functionKeyword token array (not yet implemented).

[jrfnl]

Other related to do's:

• Adjust Parentheses::getOwner() to allow for T_FN as parentheses owner in older PHPCS versions.
• Array::getDoubleArrowPtr(): Take the double arrow in arrow functions into account when searching for array double arrows.
• Take arrow functions into account anywhere and everywhere code is in place to skip (over) closed scopes.

For most of these: can't just check for T_FN, will also need to check for T_STRING with fn content and parentheses opener as next effective token.

Similar, can't just check T_FN_ARROW, but will also need to check for T_DOUBLE_ARROW preceded by parentheses, preceded by T_FN/T_STRING with content fn.