[DNR] Invalidate ruleset loads started before an extension unload

The extension version check in LoadRequestData can miss a case where an
extension is force installed with the same version as seen in the
linked bug.

This means AddRuleset can be called twice in succession if a ruleset
load from an extension is completed after the extension gets
unloaded then loaded from a force install, and the second load causes
the extension to try loading its ruleset again.

To counter this, introduce a randomly generated request id for each
load that gets invalidated if an extension unload happens after the
load starts.

Bug: 358617943
Change-Id: Ifec53afaef9304b46381e75d7a421f607d911235
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6825672
Reviewed-by: Devlin Cronin <rdevlin.cronin@chromium.org>
Commit-Queue: Kelvin Jiang <kelvinjiang@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1500416}