Matrix library improvements

[MaEtUgR]

Solved Problem

When @jwidauer helped me investigating for #22574 he had many suggestions to improve the matrix library.

Solution

Here I sorted out some low-hanging fruits he added in the code and I did some small additions.

• Include chain, don't include "math.h" everywhere and generate circular dependencies
• Slice templated on Matrix const and non-const case -> SliceT, ConstSlice
• Some simplifications to not repeat the type of the return value, using Vector3 where it makes sense, ...

Changelog Entry

Cleanup: matrix library improvements

Test coverage

Build and unit tests still work