[compiler] Remove unneeded data() accessors

Since the accessors are only called from other methods in the same
class, we can just access the field directly. This makes stepping
through easier and makes the code simpler by avoiding an unneeded
abstraction.

R=thibaudm@chromium.org

Bug: v8:12330
Change-Id: I39727324e82fcfd15b3b242c53ed5534e2e5511d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3372912Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78520}