Dependency versions should be consolidated in libs.versions.toml file / ndk version referenced dynamically

[mikehardy]

Anki-Android-Backend hasn't gotten the excellent feature forward-port of putting all version information in a libs.versions.toml file, so we have versions scattered everywhere

First step should be to consolidate versions into that single file, then the NDK install could reference the file - even from workflow .yml scripts and shell scripts etc it is trivial to parse the toml file and dynamically pull the version, so the NDK version is only defined in one spot

The README file should be altered at the same time to link to the toml file instead of referencing the version directly as it does not

Originally posted by @mikehardy in #402 (comment)

[voczi]

Re-visting this and #406 when NDK28 is out.