[MacOS] Load the AOT library via the dart bundle if it exists

[awood314]

Relevant discussion in https://github.com/flutter/flutter/issues/43454

Currently, the only way to load AOT data in macOS is through the elf snapshots, which do not get built by the current flutter tooling. Without elf snapshots, it is not possible to load multiple AOT bundles in a single application (use case described in https://github.com/flutter/flutter/issues/104144)

This change utilizes Settings::application_library_path by exposing it through the embedder API and setting it to be the executable path from the FlutterDartProject dart bundle (if it exists)

Pre-launch Checklist

• [x] I read the Contributor Guide and followed the process outlined there for submitting PRs.
• [x] I read the Tree Hygiene wiki page, which explains my responsibilities.
• [x] I read and followed the Flutter Style Guide and the C++, Objective-C, Java style guides.
• [x] I listed at least one issue that this PR fixes in the description above.
• [x] 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.
• [x] I updated/added relevant documentation (doc comments with ///).
• [x] I signed the CLA.
• [x] All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel on Discord.

[google-cla[bot]]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[chinmaygarde]

I'll take a closer look at the embedder API change. But perhaps @cbracken can take a closer look at the rest?

[skia-gold]

Gold has detected about 1 new digest(s) on patchset 18. View them at https://flutter-engine-gold.skia.org/cl/github/34062

[zanderso]

@chinmaygarde friendly ping.

[zanderso]

From PR review triage: It looks like this PR might be stale @awood314 I'm going to close this, but if you'd like to continue with it, feel free to reopen after addressing the comment from @cbracken . Thanks!