JP-3465: Use TMEASURE in resample step

[emolter]

Resolves JP-3465

Closes #8073

This PR adjusts the way exposure time weighting is computed in the resample step to use the new measurement_time keyword from JP-3449 instead of the exposure time.

Jenkins job

Checklist for maintainers

• added entry in CHANGES.rst within the relevant release section
• updated or added relevant tests
• updated relevant documentation
• added relevant milestone
• added relevant label(s)
• ran regression tests, post a link to the Jenkins job below.
  How to run regression tests on a PR
• Make sure the JIRA ticket is resolved properly

[codecov]

Codecov Report

Attention: Patch coverage is 90.00000% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 75.38%. Comparing base (4cc0ac1) to head (2791f42).
Report is 16 commits behind head on master.

Files	Patch %	Lines
jwst/resample/resample_utils.py	81.81%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8212      +/-   ##
==========================================
+ Coverage   75.15%   75.38%   +0.22%     
==========================================
  Files         470      474       +4     
  Lines       38604    38937     +333     
==========================================
+ Hits        29014    29351     +337     
+ Misses       9590     9586       -4     

Flag	Coverage Δ		*Carryforward flag
nightly	77.33% <ø> (-0.07%)	⬇️	Carriedforward from 4cc0ac1

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[hbushouse]

Code updates look good to me. Just one minor suggestion for the change log entry. I think we could go ahead and merge these changes even before you're done making updates to regtest data files. Any test inputs that don't have TMEASURE in them yet should just fall back to using EFFEXPTIM.

[hbushouse]

I wonder if we should make an update to the resample/resample_spec docs to just mention which exposure time related keyword is actually used by the step when doing "exptime" weighting. There may not be any mention of it at all in the docs right now, but given how many different flavors of time-related keywords we have in the headers, I think it's worth explicitly saying in the docs which one is used.

[emolter]

Starting new regtest run after removal of TEXPTIME keyword. Note stdatamodels install was overridden to use this branch.

[hbushouse]

The latest regression test run results look good. All failures are just the absence of TEXPTIME in combined products, as expected, and a few instances of different values for the new TMEASURE keyword. So that looks good.