Meson subproject sample test control

[piotrrak]

Hello

Currently when using as this library meson subproject I have no control over on weather tests and samples are built.

The first change bumps required meson version to 0.54.0 (ffmpeg on meson-4.3 branch already requires it). This let me remove check for meson.override_dependency() and use 0.53.0 pretty summary(). Second change leaves defaults as they were - when built as subproject it defaults to no tests and samples. While now I can specify -Davcpp:build_tests=true in my master project to adjust it to my likeing.