[runtime] Simplify TO_INT32/TO_UINT32 abstract operations.

[runtime] Simplify TO_INT32/TO_UINT32 abstract operations.

No need to provide TO_INT32/TO_UINT32 functions for every native
context, as they can be implemented in terms of TO_NUMBER more easily
and efficiently.

Also remove the obsolete TO_BOOLEAN_FUN_INDEX from the native contexts.

Review URL: https://codereview.chromium.org/1275013004

Cr-Commit-Position: refs/heads/master@{#30080}