Introduce Override Layout Behavior API

[thecoolwinter]

Description

Introduces an API to override how text is laid out by the layout manager. An API consumer can implement an object conforming to the TextLayoutManagerRenderDelegate protocol to provide custom behavior.

Introduces tests for new APIs.

Specific changes:

• Created a new TextLayoutManagerRenderDelegate which contains optional methods to override layout behavior. All methods are optional, and default to the default implementation.
• Updates the layout manager to use these methods where relevant.
  • Estimated height, line height.
  • Finding x position in a line fragment.
  • Creating a view to render a line fragment (LineFragmentView by default, but the render delegate can give a custom one).
• Makes lots of variables and methods public that weren't previously. Since we're allowing using the layout manager outside the context of a text view, these are necessarily public.
• LineFragmentView is now an open class to allow for overriding methods.
• Two methods on LineFragment have been marked as depreciated (xPos and rectFor). These were moved to the TextLayoutManger to ensure that the new render delegate can inject it's own behavior for both those methods if available.
• TextSelectionManager
  • draw method is now public, for drawing selections in a custom context.
  • Updates some methods that were calculating drawing rects to use the layout manager information, rather than text view information. This allows the selection manager's behavior to reflect overridden layout manager behavior.
• Documented exactly what layoutLines does in TextLayoutManager.
• Removed two misleading methods. ensureLayoutUntil was used once, and it was not being used correctly. preparePositionForDisplay was only used by that method. Both of these methods destroyed layout information without recourse, sometimes causing text to just disappear despite a perfectly valid layout pass.
  • ensureLayoutUntil could be added back, but needs to be implemented in a way that's additive, rather than removing layout information.
  • Removing these changes didn't effect the ability to jump to scroll positions, or emphasize text ranges.

Related Issues

• ✨ Minimap CodeEditSourceEditor#33

Checklist

• I read and understood the contributing guide as well as the code of conduct
• The issues this PR addresses are related to each other
• My changes generate no new warnings
• My code builds and runs on my machine
• My changes are all related to the related issue above
• I documented my code

Screenshots

[tom-ludwig]

Looks great! Also, big thanks for the well-written PR description—it really makes the review process smoother. Just a few minor suggestions in the documentation to improve readability.