It's unfortunate that there is both a LocalIsolate template parameter,
and an actual LocalIsolate class. Clean this up by renaming the
template parameters to IsolateT

Change-Id: Iecefc3eca5aeb7bbd21e78818b90f9e75cdff10f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2846880
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74173}