a38fb595cf
Adds JSSymbol and JSBigInt and erases to either their respective interceptor types in the JS backends or JSValue in dart2wasm. CoreLibraryReviewExempt: Backend-specific library. Change-Id: Ib2c70d22a70c6308733cd170b91eafa8ec3b3aeb Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/321749 Reviewed-by: Sigmund Cherem <sigmund@google.com>