dsl: Add functionality to intersect SubDimensions

[EdCaunt]

Introduce the ability to form a new SubDimension as the intersection of multiple SubDimensions

[codecov[bot]]

Codecov Report

Merging #2222 (c020cf3) into master (a1e4d90) will decrease coverage by 0.06%. Report is 4 commits behind head on master. The diff coverage is 6.66%.

@@            Coverage Diff             @@
##           master    #2222      +/-   ##
==========================================
- Coverage   87.11%   87.05%   -0.06%     
==========================================
  Files         228      228              
  Lines       40810    40840      +30     
  Branches     7471     7486      +15     
==========================================
+ Hits        35551    35553       +2     
- Misses       4653     4681      +28     
  Partials      606      606              

Files	Coverage Δ
devito/types/dimension.py	90.16% <6.66%> (-3.33%)	:arrow_down:

[EdCaunt]

This needs bunch of tests including with MPI. Do we wanna define union as well?

Tests to come. Union is more complex and less urgent so was going to leave for now