Refactor: Preconditioner function library

[maki49]

fix #5376

"precondition_funcs.h" is designed as a function library with following function types:

1. single-value transformer: none / qe-pw hard coded formula)
2. vector-vector operator: div(prevec) / div(trans(prevec-eig)
3. (In the future, at one's need) Matrix-vector operator

Two ways to use this library:

• Construct your own lambda / funciton with the library functions (or not), and pass it directly into the eigensolver (e.g. in module_lr)
• Construct a PreOP object to preallocate the device memory at its construction, then use .get() interface to get the function to be called by the eigensolver (e.g. in hsolver_pw)

Now this library is applied to "dav" and "dav_subspace". The precondition method of "cg" and "bpcg" seems more complicated, so I will not change them before further investigation.

[kirk0830]

@jieli-matrix Hi, do you have any suggestions on precondition operation?