iOS: Started initializing the gpu disable sync switch based on the app state.

[gaaclarke]

We've seen a few issues related to flutter apps launching in the background (flutter/flutter#76068 and flutter/flutter#71074). I've been unable to reproduce these bugs but I theorize that there is a race condition between launching the app and actually having the ability to access the GPU. In both cases it appears to be a result of the io thread using the GPU, possibly before the surface is created. This PR will make any accidental usage of the GPU fallback to the CPU if it happens before the app has actually become active.

I place a print statement in -[FlutterEngine createShell:libraryURI:initialRoute:] and it appears even during normal app launching that the app state is not active which offers further support that this is possible.

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the Flutter Style Guide and the C++, Objective-C, Java style guides.
• I listed at least one issue that this PR fixes in the description above.
• I added new tests to check the change I am making or feature I am adding, or Hixie said the PR is test-exempt. See testing the engine for instructions on
  writing and running engine tests.
• I updated/added relevant documentation (doc comments with ///).
• I signed the CLA.
• All existing and new tests are passing.
• The reviewer has submitted any presubmit flakes in this PR using the engine presubmit flakes form before re-triggering the failure.

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[gaaclarke]

I have 2 outstanding requests to verify that this addresses customer issues (since I can't reproduce the problem). I'll wait a bit longer to land to give those customers a chance to respond.

[gaaclarke]

This shouldn't hurt. I have a theory that it fixes a few issues but was unable to verify the fix. I waited around to see if I could get some feedback from customers. I'm going to land it since that will help users test it.

[mmoaay]

It seems Flutter 2.0 didn't include this PR, So will there be a 1.22.6.hotfix version to fix this problem?

[gaaclarke]

With no definitive reproduction steps it was impossible for me to know if this fixed the couple of issues I suspect it might fix. In the absence of proof I couldn't recommend it for cherry-picking.

[gaaclarke]

I've finally been able to reproduce the bug and after #24958 lands the issue should be fixed. It was a hard issue to reproduce...

cc @danielSafeNow @Wooder @luca-safenow