feat(core): return a processed spec when a new spec is compiled

[sehilyi]

Fix #
Toward #

Change List

• This PR adds an internal object as the third parameter of compile callback function:

<GoslingComponent spec={spec} compiled={(newSpec, newHg, _internalData) => {
   const { _processedSpec } =  _internalData;
}/> 

gosling.js/src/compiler/compile.ts

Lines 75 to 81 in 346a2f6

	publish('specProcessed', {
	id: specCopy.id,
	spec: specCopy
	});
	// Make HiGlass models for individual tracks
	createHiGlassModels(specCopy, trackInfos, callback, theme, urlToFetchOptions);

The _processedSpec is the same as the specCopy object above, which is the processed spec.

Checklist

• Ensure the PR works with all demos on the online editor
• Unit tests added or updated
• Examples added or updated
• Documentation updated (e.g., added API functions)
• Screenshots for visual changes (e.g., new encoding support or UI change on Editor)