Enforce uniqueness of data files in a directory.

[rwblair]

https://bids-specification.readthedocs.io/en/stable/common-principles.html#uniqueness-of-data-files
fixes #1107

Added in src/valdiators/filenameValidate.ts. This check sees if another file exists in the parent directory of the context that has the contexts exact entities and sufiix but a different valid (non-sidecar) extension from the rules.files.* rule that the context matched.

Unfortunately there is a problem with relying on the rules.files.*. It does not state which extensions are mutually exclusive. One ieeg format for instance states Each recording consists of a .vhdr, .vmrk, .eeg file triplet as valid:
https://bids-specification.readthedocs.io/en/stable/modality-specific-files/intracranial-electroencephalography.html#ieeg-recording-data
https://github.com/bids-standard/bids-specification/blob/master/src/schema/rules/files/raw/ieeg.yaml

Maintaing list of sidecar extensions in filenameValidate.ts is no good and should probably be pulled from the schema if possible.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.25%. Comparing base (a4e1a09) to head (a16a234).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2071      +/-   ##
==========================================
+ Coverage   85.69%   87.25%   +1.55%     
==========================================
  Files          91      139      +48     
  Lines        3782     6763    +2981     
  Branches     1220     1600     +380     
==========================================
+ Hits         3241     5901    +2660     
- Misses        455      772     +317     
- Partials       86       90       +4     

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[effigies]

We should check that .eeg+.vhdr+.vmrk don't trigger this.

Also, there is bids-standard/bids-specification#1492. Might be worth getting that working again and using that? I believe the schema was in good shape and the rendering code just gathered merge conflicts.