Mark the labels to the code and data global, which removes the need
for having separate pointers to these labels in the .data section.

This means that `v8_Default_embedded_blob_code_` and
`v8_Default_embedded_blob_data_` can now actually be read-only when
RELRO is enabled.

The actual contents of `v8_Default_embedded_blob_code_` remain
potentially non-readable for platforms where code is marked as
execute-only, but these changes do not attempt to read them.

Bug: v8:12850

Change-Id: Ic1bc8e68fe44a9ce45380c83b0be5fa94e7da267
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3616510
Commit-Queue: Georgia Kouveli <georgia.kouveli@arm.com>
Reviewed-by: Jakob Linke <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80331}