[feature] CMakeToolchain + Android POC

[memsharded]

Implement a proof of concept of using the new CMakeToolchain feature for building:

• Android projects (from Linux/OSX)
• From Windows

Notes:

• Android NDK can be assumed installed
• Focused on creating/building 1 package, both local flow (conan install + native cmake) and conan create flow.
• Integration test.
• Test can be skipped for CI, but should work locally, annotate assumptions and installation details
• No env-var configuration at all
• All code must be private and local to the toolchains package
• New cross-build model with contexts must be used if necessary, not the old os_build, arch_build
• If enough time to implement reuse of a package, the cmake_find_package_multi generator must be used