Changes to the instructions for interpreting tests will likely produce
new failures for consumers who are updating between revisions of
Test262. Introduce a machine-readable convention for signaling
substantive changes.

https://github.com/tc39/ecma262/pull/988 changes the iteration protocol
such that the "next" method is only loaded from the iterator object once
during the prologue of iteration, rather than during each step.

BigInt.asUintN tests

Change destructuring tests to not rely on exact evaluation order for property references

Fixes #1202

* typeCoercion.js supports ToIndex
* typeCoercion.js supports ToBigInt
* updated BigInt.asIntN type coercion tests to use typeCoercion.js

Tests for ECMA 402 PR https://github.com/tc39/ecma402/pull/170
The tests on Date/DateTimeFormat are valid without the PR.

type coercion harness utilities + features flags + linting

features: update all features flags for all test files with harness/* deps that require a feature flag