[Impeller] Switch SolidStrokeContents to use solid fill shaders; remove solid stroke shaders

[bdero]

This is another step towards removing the special sauce from solid stroke rendering. See also: https://flutter.dev/go/impeller-geometry#heading=h.fymtgh4bhdl2

[flutter-dashboard]

It looks like this pull request may not have tests. Please make sure to add tests before merging. If you need an exemption to this rule, contact Hixie on the #hackers channel in Chat (don't just cc him here, he won't see it! He's on Discord!).

If you are not sure if you need tests, consider this rule of thumb: the purpose of a test is to make sure someone doesn't accidentally revert the fix. Ask yourself, is there anything in your PR that you feel it is important we not accidentally revert back to how it was before your fix?

Reviewers: Read the Tree Hygiene page and make sure this patch meets those guidelines before LGTMing.

[jonahwilliams]

LGTM

[jonahwilliams]

I don't know if these tasks are going to finish . If you push an empty commit, that should unclog it...

[bdero]

Whoops, thanks. This fell off my radar.

[auto-submit]

auto label is removed for flutter/engine, pr: 36624, due to - The status or check suite Linux Web Framework tests has failed. Please fix the issues identified (or deflake) before re-applying this label.