Refactor Android property key CStr construction to add tests

[lopopolo]

Add a new FFI utils module that is always tested on all platforms.

Extract the C string bytes to a const and getter function, add more docs, add tests that the const can be safely turned into a CStr.

[astraw]

Looks good. Thanks.

[Kijewski]

I updated the CI to make sure the test is executed, because I don't think anyone of us will want to try every commit on our actual phones. :)

[lopopolo]

@astraw @Kijewski I took another stab at this to reduce some of the complexity in CI and add more tests + additional safety checks in CI and debug mode.

[Kijewski]

I added Tier- to Tier-3 labels to match https://doc.rust-lang.org/nightly/rustc/platform-support.html. E.g Android is a Tier 2 platform.

[lopopolo]

Alright we have two approvals, I've addressed all of the comments, and the build is green. Since this has the Unsafe-Proposed label, I'll merge this on October 7.

[lopopolo]

I added Tier- to Tier-3 labels to match https://doc.rust-lang.org/nightly/rustc/platform-support.html. E.g Android is a Tier 2 platform.

Thanks for this! I went through the full history of PRs and issues and added these tags the best I could.

[astraw]

Great, thanks @lopopolo .

This is now ready to merge. Given its Unsafe-Proposed status, the 7 day timer starts now. So we should merge this on 8 October.

[astraw]

(@lopopolo somehow I missed your earlier message about merging on 7 October. Sorry about that!)