Add yield expression test

[tihiera]

Adds a conversion test for yield_expression, covering both yield and yield* (delegate). This construct was supported in the IR (JsirYieldExpressionOp) but had no conversion test.

Test files were generated using generate_tests.py. The test verifies:

• JS source → AST parsing
• AST → JSHIR lowering (including the delegate attribute)
• Full roundtrip: source → AST → JSHIR → AST → source

[phisiart]

Thanks for the PR! This repo is automatically sync'ed from our internal codebase, so let me figure out a way to check in your PR without breaking the sync process (similar to #48).