Bug 1875867 [wpt PR 44122] - Add multidimensional variants to test generator for...

Bug 1875867 [wpt PR 44122] - Add multidimensional variants to test generator for blur filter tests, a=testonly

Automatic update from web-platform-tests
Add multidimensional variants to test generator for blur filter tests

Variants in the test generator enable the creation of different versions
of a test while using the same main test body. Until now, variants had
to be a single set of scenarios for the test, for them to be generated
one by one. This change adds a `variant_matrix` parameter that can
receive several variant sets as input, and generates tests using every
possible combination by selecting an option from each variant (like the
Cartesian product of the sets).

In this version it is not possible to use both the existing `variants`
parameter and the new `variant_matrix` parameter at the same time.

To support flexible naming structures with variants, the generator now
exposes the different variant names used as an array that can be used
as a jinja variable, and a parameter (`append_variants_to_name`) that
disables the automatic appending of variant names at the end of the
test name.

The test for the `gaussianBlur` filter now uses this `variant_matrix` to
keep its existing variants and also test all of them both with layers
and `CanvasFilter` objects.

`gentestutilsunion.py` was formatted with `git cl format` by
commenting the line that excludes web_tests/external/wpt:
https://source.chromium.org/chromium/chromium/src/+/main:.yapfignore;l=6

Bug: 1396372
Change-Id: Iad108fe5c079ce8cebe365f2b5f4ad6e71599c9c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5213287
Commit-Queue: Andres Ricardo Perez <andresrperez@chromium.org>
Reviewed-by: Yi Xu <yiyix@chromium.org>
Reviewed-by: Jean-Philippe Gravel <jpgravel@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1266476}

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wpt-commits: 75bf02c77adecba140b1a0cb59b5d1170086d9e5
wpt-pr: 44122