Evaluate extension point on track config pre-process snapshot

[cmdcolin]

This could possibly be a method for plugins to set 'default' values in track configs xref #3609

The extension point is named Core-preProcessTrackSnapshot and plugins could addToExtensionPoint('Core-preProcessTrackSnapshot',snap=>/*manipulate snap;return snap*/)

I considered adding this to other config snapshot pre-processors but not all of them have a pluginManager available (e.g. the display one does not)

Could adjust to make that available, or accept that only track level is available?

[codecov]

Codecov Report

Merging #3653 (4c8305d) into main (c155f5c) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head 4c8305d differs from pull request most recent head 1a824ab. Consider uploading reports for the commit 1a824ab to get more accurate results

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##             main    #3653   +/-   ##
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  Coverage   63.06%   63.07%           
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  Files         877      877           
  Lines       30167    30167           
  Branches     7272     7272           
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+ Hits        19026    19028    +2     
+ Misses      10956    10954    -2     
  Partials      185      185           

Impacted Files	Coverage Δ
...re/pluggableElementTypes/models/baseTrackConfig.ts	58.33% <100.00%> (ø)

... and 1 file with indirect coverage changes

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[rbuels]

I'd recommend adjusting things to make the pluginManager available where possible. We want to make a lot of extension points that people can manipulate in a lot of different places.

[cmdcolin]

@rbuels it would possibly be somewhat of a 'breaking change' in some cases if we added a pluginManager param to the config schemas like e.g. the baseLinearDisplayConfigSchema, since they are re-exported from the package for use by plugins. could either keep those as is or just accept a breaking change...

[rbuels]

I seem to vaguely remember we make the pluginManager available in the MST environment, can snapshot preprocessors get it from that?

[cmdcolin]

getEnv does not work in preProcessSnapshot, there is no "self" to getEnv on as far as i could tell