Previously we'd hold on to Script objects strongly after they are
considered unreachable by V8 itself, and keep them around for the
V8DebuggerAgent cache (whose upper limit can be controlled with a
parameter to `Debugger.enable`).

This CL changes that to instead copy out the script source and the
WebAssembly bytecode (depending on whether it's JavaScript or Wasm)
to the C++ heap and keep it cached there.

Fixed: chromium:1295659
Bug: chromium:1246884
Change-Id: Idfcd7172715eafca6b011826ae03a573d58803f2
Doc: https://bit.ly/v8-inspector-script-caching
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3472082Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79217}