Add subspace diagonalization for orthogonal input

[Cstandardlib]

Linked Issue

Fix #5615

Description

• diagH_subspace is used in hsolver to do a diagonalization in the subspace spanned by given psi vectors.
• When input vectors are orthogonal, there is no need to do the overlap and solve generalized eigenvalue problems.
• Add a parameter to support this procedure without assigning and calculating overlap block.
• Remove need_subspace parameter not needed in dav_subspace code.

[mohanchen]

LGTM, I think we should add unit tests for these functions.

[Cstandardlib]

@mohanchen OK,I'll add tests for this set of functions.