DevTools: Implement waitForDebuggerOnStart for SharedWorker auto-attach

Fix `waitForDebuggerOnStart` for SharedWorker auto-attach by aligning
its implementation with `ServiceWorkerDevToolsManager`.

An `Observer` pattern, modeled on the one in
`ServiceWorkerDevToolsManager`, is added to
`SharedWorkerDevToolsManager`. This allows the `BrowserAutoAttacher` to
intercept worker creation and enforce the pause, preventing a race
condition with injected scripts.

Bug: 428100629
Change-Id: Iab60d14d30dd0a0e8634ca7637737ee5c21ecf8e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7037151
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Dmitry Gozman <dgozman@chromium.org>
Auto-Submit: Wang Neden <nedenwang@gmail.com>
Reviewed-by: Alex Rudenko <alexrudenko@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1529406}