Simplify ti.Matrix

[strongoier]

Currently ti.Matrix has become a single class with more than 1000 lines, with all deprecated/obsolete/unused/rarely used features mixed together. For better code maintainability, we need to carefully decide what should be exposed to users and clean up this class.

[victoriacity]

I'd recommend moving the linear algebra methods (inverse(), diag(), determinant()) to linalg.py so that we have a clear distinction between API and math implementations. For example, matrix.inverse() will become an alias of ti.inverse(matrix), similar to NumPy ndarrays and PyTorch tensors.