Bug 1813292 [wpt PR 38239] - Allow speculative parser to see inside DSD templates...

Bug 1813292 [wpt PR 38239] - Allow speculative parser to see inside DSD templates, a=testonly

Automatic update from web-platform-tests
Allow speculative parser to see inside DSD templates (#38239)

Prior to this CL, the speculative parser would bail out at the sight
of any <template> element. However, if that template was a DSD
shadow root, like <template shadowrootmode=open>, it should be
scanned.

Note that DSD shadow roots inside "normal" template elements
should still be skipped, since everything in the <template>
is inert.

I also updated the speculative parser script to not blow away *all*
files, but instead just remove the .html files.

Bug: 1379513
Change-Id: I0ee8d64d9c33905f9fb1c5a0f5b4f428858c403a
Fixed: 1410933
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4200836
Commit-Queue: Mason Freed <masonf@chromium.org>
Reviewed-by: David Baron <dbaron@chromium.org>
Auto-Submit: Mason Freed <masonf@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1100556}

Co-authored-by: Mason Freed <masonf@chromium.org>
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wpt-commits: 762a5fb8c064671367435e2e3db21f231ea8b2c2
wpt-pr: 38239