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[bot]]

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 :warning:

Additional details and impacted files

```diff @@ 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]

GTG!