[Impeller] Report pipeline creation feedback to logs and traces.

[chinmaygarde]

Piping the feedback to logs is disabled by default but can be enabled by patching the source for now. If reading from logs gets to be useful, we can move it behind a flag. In traces, enabled by default, pipeline cache hits and misses will be shown via counters. The time taken to create a pipeline variant is already covered by existing traces.

This patch also sets up infrastructure in the impeller::CapabilitiesVK to quickly enable optional device extensions.

Pipeline feedback will only be reported if the device supports VK_EXT_pipeline_creation_feedback.

Example of logs:

E/flutter ( 2011): >>>>>>
E/flutter ( 2011): Pipeline 'GaussianBlurAlphaDecal Pipeline' Time: 48.60ms Cache Hit: 0 Base Accel: 0 Thread: 481449901232
E/flutter ( 2011):  Stage 1: Time: 12.91ms Cache Hit: 0 Base Accel: 0 Thread: 481449901232
E/flutter ( 2011):  Stage 2: Time: 15.10ms Cache Hit: 0 Base Accel: 0 Thread: 481449901232
E/flutter ( 2011): <<<<<<

[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]

What is the switch I'd need to flip to see the feedback locally?

[chinmaygarde]

Set kReportPipelineCreationFeedbackToLogs to true.

[jonahwilliams]

ahh I missed that, makes sense

LGTM