Fix vegetation temperature weighting during phenology

[rgknox]

Description:

This change improves how we calculate vegetation temperature during phenology. The previous method included bare ground patches in the mean. Bare ground temperatures are initialized with the column/site level air temperature, but those values are not as representative of using only patch level vegetation temperatures. This new method filters in only temperatures from patches with vegetation, and uses the canopy area as the weighting factor, instead of total patch area.

This should precede #1226

Collaborators:

@rosiealice

Expectation of Answer Changes:

Yes, this should change answers, at least for tests that are long enough to trigger phenology events.

Checklist

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All checklist items must be checked to enable merging this pull request:

Contributor

• The in-code documentation has been updated with descriptive comments
• The documentation has been assessed to determine if updates are necessary (NOT NECESSARY)

Integrator

• FATES PASS/FAIL regression tests were run
• Evaluation of test results for answer changes was performed and results provided

Test Results:

TBD

CTSM (or) E3SM (specify which) test hash-tag:

CTSM (or) E3SM (specify which) baseline hash-tag:

FATES baseline hash-tag:

Test Output:

[glemieux]

This looks straightforward.