[Select To Speak] Rename MV2 javascript tests

Partial reland of reverted:
6393804: Revert "[Select To Speak] Build both mv2 and mv3 extension, add flag" | https://chromium-review.googlesource.com/c/chromium/src/+/6393804

Breaking into smaller changes to find source of regression.

This change only updates the names of javascript tests in preparation for the period when we will run two sets of tests, those in the MV2 directory and the MV2 directory.

Bug: 388867837
Change-Id: Ia1e84bf2e29e4da042bf9b950279661da3337eca
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6423195
Reviewed-by: Akihiro Ota <akihiroota@chromium.org>
Commit-Queue: Valerie Young <spectranaut@igalia.com>
Cr-Commit-Position: refs/heads/main@{#1441539}