Set the `--enable-change-array-by-copy` shell flag and the
`javascript.options.experimental.enable_change_array_by_copy` pref to true
by default in all builds.

Remove the `--enable-change-array-by-copy` build flag from `js/moz.configure`
and make all code previously guarded by `#ifdef ENABLE_CHANGE_ARRAY_BY_COPY`
compile unconditionally.

Remove `change-array-by-copy` from testing build configurations (non262
and jit-test tests are no longer guarded with
`getBuildConfiguration()['change-array-by-copy']`

Remove all code from test config files that sets
`javascript.options.experimental.enable_change_array_by_copy`; only
`StaticPrefList.yaml` should set this pref.

Fix non262 unscopables test that apparently wasn't running before to use
the correct names for change-array-by-copy methods

Remove the `TypedArray` property from `gPrototypeProperties` in
`test_xrayToJS.xhtml`, as this property was written but never read.

Differential Revision: https://phabricator.services.mozilla.com/D174699