[devtools] Import test runners in http/tests/devtools/coverage

This CL replaces 'TestRunner.loadTestModule' calls with import
statements.

Also updates 1 test in:
  * http/tests/devtools/console-sidebar

The CL was fully auto-generated by a small regex search&replace script.

Note that 2 tests needed to be re-baselined due to line numbers
referencing the test files themselves.

R=jarin@chromium.org

Bug: 1442410
Change-Id: I32b479069e30d7a28495702cc8f5097c2939d3f2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4531943
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Simon Zünd <szuend@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1144023}