Create extension point for session model

[elliothershberg]

This is a tiny PR from an idea that @cmdcolin and I worked on. It is related to #2032, but is for the session model, instead of the state model on a display type. This was motivated by work on #2080 .

Here, before the session model is returned from the model factory, it checks if any plugins have an extendSession method defined. If it does, it updates the session model with the result of that function.

For example:

extendSession(sessionModel: IAnyModelType) {
  return types.compose(
    sessionModel,
    types.model('HelloWorld', { foopy: types.optional(types.string, 'lol') }),
  )
}

Would extend the session with the new attribute foopy.

We also investigated doing something similar for the LGV menu, but ran into some issues so stopped here for now. Would be curious about your thoughts @rbuels and @garrettjstevens .

[codecov]

Codecov Report

Merging #2120 (1e65a98) into main (b223419) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #2120   +/-   ##
=======================================
  Coverage   62.02%   62.02%           
=======================================
  Files         476      476           
  Lines       22789    22793    +4     
  Branches     5350     5350           
=======================================
+ Hits        14134    14138    +4     
  Misses       8374     8374           
  Partials      281      281           

Impacted Files	Coverage Δ
packages/core/Plugin.ts	100.00% <100.00%> (ø)
products/jbrowse-web/src/sessionModelFactory.ts	59.32% <100.00%> (+0.25%)	⬆️
packages/core/util/index.ts	79.89% <0.00%> (ø)

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[garrettjstevens]

What would be a use case for this? If you're adding a pluggable element (like a view or widget), it has its own model that it can store things on, and that model will be in the session, so I'm not sure why we need an extra way to extend the session model.

[elliothershberg]

What would be a use case for this? If you're adding a pluggable element (like a view or widget), it has its own model that it can store things on, and that model will be in the session, so I'm not sure why we need an extra way to extend the session model.

The use case this was written for was that when I tried to store bookmarks in the widget's model in #2080 , the values didn't persist. I may have been doing something wrong?

I think I'm going to close this draft in favor of a more general extension points implementation @rbuels and I just worked on, which can accomplish this also.

[elliothershberg]

Closed in favor of #2140