Progresses #1279.

Summary

• brings interpreter property descriptors much closer to the compiled runtime across ordinary objects, arrays, functions, built-ins, and exotic carriers
• fixes receiver binding and spec coercion gaps exposed by the full Test262 run
• keeps mutable RegExp prototype function metadata isolated per realm
• adds focused parity coverage and synchronizes both Test262 baselines

Differential parity

before                         after
2275 Fail -> Pass              1591 Fail -> Pass
1263 RuntimeError -> Pass       670 RuntimeError -> Pass
 675 RuntimeError -> Fail       242 RuntimeError -> Fail
 119 Fail -> RuntimeError       228 Pass -> Fail
  84 Pass -> Fail               140 Fail -> RuntimeError
  31 Pass -> RuntimeError       106 Pass -> RuntimeError
  18 Fail -> HarnessError        18 Fail -> HarnessError
   1 Fail -> Timeout              3 Timeout -> Fail
   1 Pass -> Timeout              1 Fail -> Timeout
                                   1 Pass -> Timeout

The increased interpreted-Pass/compiled-failure buckets expose the next Track B compiler work; total disagreement still drops by 32.8%.

Validation

• dotnet test SharpTS.sln --no-restore: 16,217 passed
• joint compiled/interpreted Test262 regeneration with four workers: 186 passed, 4 diagnostic skips, 0 failed
• issue parity tests: 164 passed