Add tests for Generator.prototype.return() with yield in finally

[taras]

Closes #4937

These tests cover the scenario where generator.return() is called while the generator is paused in a try block, and the finally block contains a yield statement. The existing tests don't cover this path:

• try-finally-within-try.js: finally has no yield
• try-finally-within-finally.js: generator already paused at yield in finally

New tests:

• try-finally-yield-triggered-by-return.js: basic yield in finally during return
• try-finally-nested-yields-triggered-by-return.js: nested try-finally with yields
• try-finally-yield-resume-value-during-return.js: resume value to yield in finally
• try-finally-throw-before-yield-during-return.js: throw before yield in finally
• try-finally-throw-after-yield-during-return.js: throw after yield in finally
• try-finally-yield-star-during-return.js: yield* in finally during return
• try-finally-yield-star-delegation-return.js: yield* delegation with finally
• try-finally-return-overrides-during-return.js: return in finally overrides value

All tests validated against V8 (Node.js), SpiderMonkey (Firefox), and JavaScriptCore (Safari).

This coverage gap was discovered while fixing a bug in Sobek (grafana/sobek#115), a Go-based JavaScript runtime.