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.

Author: eric-wieser

src/linear_algebra/bilinear_form.lean

@@ -6,6 +6,7 @@ Authors: Andreas Swerdlow, Kexing Ying
 
 import linear_algebra.dual
 import linear_algebra.matrix.basis
+import linear_algebra.matrix.nondegenerate
 import linear_algebra.matrix.nonsingular_inverse
 import linear_algebra.tensor_product