[WIP] Add water content as a composition to subducting plates

[danieldouglas92]

Due to a change in the implementation, PR #661 has been closed and has been repurposed in this PR. The goal is the same, but the issue with the implementation in the previous PR is that the water content at a given point within the slab did not depend on what the water content was at points updip. This new implementation accounts for the history of a given point within the slab by iterating along a plane at a fixed depth from the slab surface from the trench to the current point, comparing the water content with each iteration to the previous iteration. The method currently used is poorly optimized, but gives the desired result.

• Implement Tian et al., 2019 parametrizations
• Implement water content into linear slab segments
• Implement water content into variable dip slab segments
• Create tests

[codecov]

Codecov Report

Attention: Patch coverage is 15.34653% with 171 lines in your changes missing coverage. Please review.

Project coverage is 96.01%. Comparing base (2361838) to head (ecba7bd).
Report is 199 commits behind head on main.

Files with missing lines	Patch %	Lines
source/world_builder/utilities.cc	5.67%	133 Missing ⚠️
...bducting_plate_models/composition/water_content.cc	22.91%	37 Missing ⚠️
source/world_builder/features/subducting_plate.cc	91.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #690      +/-   ##
==========================================
- Coverage   98.23%   96.01%   -2.23%     
==========================================
  Files         107      108       +1     
  Lines        7464     7670     +206     
==========================================
+ Hits         7332     7364      +32     
- Misses        132      306     +174     

Files with missing lines	Coverage Δ
source/world_builder/features/fault.cc	99.66% <100.00%> (+<0.01%)	⬆️
...res/subducting_plate_models/composition/uniform.cc	100.00% <ø> (ø)
source/world_builder/features/subducting_plate.cc	99.36% <91.66%> (-0.31%)	⬇️
...bducting_plate_models/composition/water_content.cc	22.91% <22.91%> (ø)
source/world_builder/utilities.cc	79.24% <5.67%> (-17.98%)	⬇️

... and 1 file with indirect coverage changes

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[danieldouglas92]

This functionality is now being merged in PR #661