When the call/usage is not found in `allowIn`, report error

[spaze]

Given a configuration like this for example:

	disallowedFunctionCalls:
		-
			function: 'pcntl_*()'
			allowIn:
				- vendor/foo/bar/Baz.php

when any pcntl call is not found in vendor/foo/bar/Baz.php, report error and suggest removing the allowIn item to keep the config clean and up to date.

This is similar to what PHPStan reports when a ignoreErrors error wasn't hit.

[spaze]

Maybe this could be rescoped to checking whether the values in allow[...] directives do exist, because with the addition of the other allowIn[...] directives (e.g. allowInInstanceOf), when the pcntl call wouldn't be find now, it doesn't really mean the allow[...] configuration should be removed. The configuration says what is legal, but it doesn't need to be necessarily used.

So possibly create a collector that would collect all files, classnames, attributes etc. where pcntl would be called (as per all the allow[...] directives) and then check whether these files, classes etc. at least exist?