Now, the CodeAssembler can annotate Nodes with SourcePositions.
SourcePositions themselves get a new mode "external," in which
they get a file_id, line and column. The file_id is currently
maintained in the isolate, mapping to strings for filenames.

Additionally, inlining information is ignored at this point,
but in the long run I'd like to recognize calls to different
CSA functions as manual inlinings.

At this point, if you want to see the results in tools like GDB,
you'll need to build without clang, and use the GCC toolchain.
GN flag is_clang=false will do the trick.

Bug: v8:8418
Change-Id: I123cdc041612285fa7d0ba532a625bceeda5d338
Reviewed-on: https://chromium-review.googlesource.com/c/1322954
Commit-Queue: Michael Stanton <mvstanton@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59009}