Audit all "esid: pending" tests

[ptomato]

esid: pending was used to indicate a test for functionality that was accepted but not yet merged into the ECMA-262 main branch.

According to git grep there are 331 tests in the tree with esid: pending. At a quick inspection most of these are actually not pending anymore, so these should be audited and given a proper esid if appropriate.

Going forward we'd like to use two mechanisms to indicate tests for items that are pending to be merged into the spec. Stage 3 proposals or other big items should use feature flags, and we will add a list of feature flags that represent features that aren't yet merged into the spec. Every test with a feature flag in this list should be considered the same as if its esid was pending.

This way, we don't have to do manual bookkeeping of individual esids for proposals when they get merged, but are still free to use esid: pending to indicate small groups of tests corresponding to a needs-consensus PR that has reached consensus but isn't merged yet.

We should also document esid: pending in the instructions for executing tests — I wasn't aware of it before today.