Implementing Clinopyroxene (CPX) slip systems into the DRex CPO plugin

[magmaxt]

Pull Request Checklist. Please read and check each box with an X. Delete any part not applicable. Ask on the forum if you need help with any step.

Describe what you did in this PR and why you did it. (related issue #3885)

1. I tested both the old LPO and the new CPO plugins for calculating Olivine A,B,C,E fabrics under simple shear. The results are consistent with Fraters and Billen 2021. Published results using LPO: Old LPO and new CPO results:

2. I added CPX slip systems into the DRex CPO plugin and reproduced the three types of fabrics from lab experiments (Zhang et al., 2006)and observed xenolith fabrics.

3. The code now work with both Olivine and CPX.[todo] further simplify the code.

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[bangerth]

Just to make sure, you closed this pull request because you're going to break it into pieces?

[magmaxt]

Just to make sure, you closed this pull request because you're going to break it into pieces?

Sorry for the late reply, I completely missed your message and thanks for checking in! Yes, I am working on a cleaner version of this pull request based on Rene's advice and will reopen a PR this week.