Moves createMochaInterface and TestStateProvider to test/conductor/ so
custom Mocha test interfaces can be reused across e2e, harness, and perf
test suites.

This CL also replaces the old mocha-interface harness used by the
cxx_debugging extension in their e2e tests.

Cq-Include-Trybots: luci.devtools-frontend.try:cpp_debug_extension_e2e_dbg,cpp_debug_extension_e2e_rel
Bug: 535748259
Change-Id: I8a1a5e5f8e97fbeca83048d95cc6e929277fcd89
TAG=agy
CONV=903602d9-99bb-4972-89b8-b0d46798477f
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/8129921
Commit-Queue: Alex Rudenko <alexrudenko@chromium.org>
Auto-Submit: Simon Zünd <szuend@chromium.org>
Reviewed-by: Alex Rudenko <alexrudenko@chromium.org>