[TS] Execute default export expressions during module initialization

[CaelmBleidd]

Summary

• Evaluate export default <expression> in source order in the module %dflt method.
• Store the result once in the static default field and point export metadata to that snapshot, so later writes to the source variable do not change the default export.
• Preserve an explicit unsupported diagnostic for bare class/function/enum/namespace declaration identifiers because EtsIR does not yet represent those declarations as standalone values.

Fixes #378.

Checks

• npm run typecheck
• npm test (218 TypeScript frontend tests)
• Focused EtsTsFrontendTest for bundled frontend JSON deserialization and model conversion
• EtsExportTest (8 tests)
• Normal checkLicense pre-commit hook

The regression compares the sample's result with TypeScript's CommonJS output in Node (default === 1, after === 10), and separately checks the corresponding EtsIR call, assignment, and source order. The Kotlin integration test checks the production JSON path. No EtsIR runtime execution is claimed.

[github-actions]

Test Results

  225 files  ±0    225 suites  ±0   16m 1s ⏱️ + 1m 36s
  788 tests +7    776 ✅ +7  12 💤 ±0  0 ❌ ±0 
2 058 runs  +7  2 008 ✅ +7  50 💤 ±0  0 ❌ ±0 

Results for commit 3c62f61. ± Comparison against base commit 873f8e9.

♻️ This comment has been updated with latest results.