compiler: Remove counters from subdomains and automatically generate unique names

[EdCaunt]

Rather than using counters to ensure subdimensions etc are unique, they should be dynamically renamed during compilation.

Supersedes #2405 .

[codecov]

Codecov Report

Attention: Patch coverage is 98.18182% with 3 lines in your changes missing coverage. Please review.

Project coverage is 87.07%. Comparing base (28e5ef2) to head (6ed3979).
Report is 18 commits behind head on master.

Files with missing lines	Patch %	Lines
devito/ir/equations/algorithms.py	95.52%	0 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2431      +/-   ##
==========================================
+ Coverage   87.00%   87.07%   +0.06%     
==========================================
  Files         239      239              
  Lines       45028    45117      +89     
  Branches     8406     8427      +21     
==========================================
+ Hits        39177    39285     +108     
+ Misses       5116     5100      -16     
+ Partials      735      732       -3     

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[FabioLuporini]

This is looking so good

[FabioLuporini]

GTG!