Wrapper for LAPACK.trevc
Provides diag, eig, eigfact eigvals and eigvecs for upper and lower Triangular matrices

Addresses #3688
- Also provides simple wrappers around the full routines for svd, svdfact, svdfact!, svdvals, svdvecs for Triangular
- Adds convert routine from Triangular to dense Matrix
- Clean up bidiagonal Matrix tests