1969330 - Include --tag=webextensions in --preset=webextensions

Status: NEW

(WebExtensions :: General, task, P3)

Description

[Rob Wu [:robwu]]

Most of the WebExtensions tests are in specific directories already covered by the webextensions preset from bug 1856473:
https://searchfox.org/mozilla-central/rev/c66e658296cd024ee6ab8330350bfde7c1f05d38/tools/tryselect/try_presets.yml#334-353

Some tests relevant to WebExtensions and add-ons in general are however located outside these directories, but they can be tagged with --tag=webextensions: https://searchfox.org/mozilla-central/search?q=tags+%3D+%22webextensions&path=toml&case=false&regexp=false
Out of these tests, only those in the devtools/client/aboutdebugging/tests/browser/ are not already matched by the existing pattern: https://searchfox.org/mozilla-central/rev/c66e658296cd024ee6ab8330350bfde7c1f05d38/devtools/client/aboutdebugging/test/browser/browser.toml#30-61

To increase the breadth of test coverage, we should look into adding --tag=webextensions to the command to run the relevant tests on try. When doing this, we should make sure that we add to the set of existing tests, and not restrict to only tests tagged with webextensions.
It would also be nice if we also document the command to run the relevant tests locally.