Unify the signatures of decomp.bidiag, decomp.tridiag_sym, and decomp.hessenberg

[pnkraemer]

Currently, all three functions return similar outputs but (needlessly) differ in their arguments.
For example, bidiag assumes a normalised input, but the other two normalise inputs internally and return lengths of inputs.

I suggest implementing a test that asserts that their outputs are identical if called in settings where the outputs are expected to be identical and fixing all mismatches until this test passes.

For instance, if we call hessenberg with a symmetric matrix, all outputs should match that of tridiag_sym,
and if we call tridiag_sym with a matrix $A=X^\top X$ and bidiag with $X$, the outputs should match, too.
As a result, users will have a much easier time switching between methods.