mathlib3

2a32c70c - refactor(linear_algebra/matrix/nonsingular_inverse): split out files for adjugate and nondegenerate (#9974)

refactor(linear_algebra/matrix/nonsingular_inverse): split out files for adjugate and nondegenerate (#9974) This breaks the file roughly in two, and rescues lost lemmas that ended up in the wrong sections of the file. The module docstrings have been tweaked a little, but all the lemmas have just been moved around.