Add ability to allow list instance methods on the script class

[jdconrad]

This change adds support to allow list instance methods on the script class in Painless and super classes of the script class. It works the same way as allow listing works now for other classes.

Example:

Allow list:

class org.elasticsearch.painless.ThisTests$TestThisBaseScript @no_import {
  String baseString();
}


class org.elasticsearch.painless.ThisTests$TestThisScript @no_import { // extends TestThisBaseScript
  String testString();

Script:

baseString() + testString() // 'base' and 'test'

Result:
basetest

[elasticmachine]

Pinging @elastic/es-core-infra (Team:Core/Infra)

[stu-elastic]

Very nice.

[jdconrad]

@stu-elastic Thanks for the review. Will commit as soon as CI passes.

[elasticsearchmachine]

💚 Backport successful

Status	Branch	Result
✅	7.x