Import test runners in http/tests/devtools/sources/debugger-async

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

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

Bug: 1442410
Change-Id: I55758efb3b260882a2c2d5ec38d7218ece63bcb7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4561933


Commit-Queue: Simon Zünd <szuend@chromium.org>
Reviewed-by: Wolfgang Beyer <wolfi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1148942}