[Core] Improve performance on AstResolver and ClassLikeAstResolver

[samsonasik]

Currently, we have isset() to verify that collection of class/method exists, but that doesn't match when previous search saved as null data, eg:

rector-src/src/PhpParser/AstResolver.php

Lines 173 to 174 in 84faf29

	// to avoid parsing missing function again
	$this->functionsByName[$functionReflection->getName()] = null;

the isset() will always got false result when it fill null value, this PR change to use isset() early, then apply array_key_exists as fallback so it will use the null value as is when it found,

see https://3v4l.org/JrQ9n

[samsonasik]

All checks have passed 🎉 @TomasVotruba it is ready for review.

[samsonasik]

I applied isset() check early, array_key_exists() as fallback in case the null data exists 👍

[samsonasik]

All checks have passed 🎉 @TomasVotruba I think it is ready.

[TomasVotruba]

Thank you 👍