Allow compiling with Rust code

[louwers]

Continuation of #2647

• Adds optional support for Rust code in the source tree. Replaces csscolorparser.hpp with a Rust library by way of proof-of-concept. Use -DMLN_USE_RUST=ON with CMake or ://use_rust with Bazel. Tested with macOS, iOS and Android.
• Generated sources headers and sources are not checked into source control. Generation integrated with Bazel and CMake.
• Rust code is licensed under the same license as the rest of the codebase.
• Test coverage on CI (Linux, CMake) is included.

Context of this PR: have Rust build tooling set up, so we are able to integrate a Rust library when the opportunity arises. Give people a playground to toy around with integrating Rust code or writing extensions for MapLibre Native in Rust.

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Open TODOs:

• Generate C++ sources during build with CMake and Bazel.
• Set up pre-commit for rustfmt.
• Already split into modules. Suggestion from @ianthetechie
• Add a smoke test to CI, see if it Rust stuff compiles on Linux. Remove other CI config for now.
• Figure out why iOS simulator toolchain does not seem to be available...

[ianthetechie]

Fantastic work, guys 🚀 I can confirm all is working on my machine with the latest (and tested making some changes to the Rust code to ensure that it's actually being used; good suggestion @louwers)!

[nyurik]

awesome work, thanks @louwers !