Add Pen and Path tool modes to avoid showing all handles

[4adex]

The objective was to provide 3 (2 in case of pen tool) modes for the viewer that changes how the handles are shown of the selected anchors. The specific requirements and intended behaviour is well written in the issue which this closes #2261.
The approach is summarised below -

• Added overlay_mode_type in options of both tools which can be modified by the radio buttons in the tool options layout.
• For each tool they are enum which control the behaviour in Overlays tool message.
• path_overlays is made more modular by giving another argument, which specifies whether all handles, specific handles, frontier handles, or no handles to be drawn.
• get_selected_segments is for getting the vector of segmentIds of all segments which are associated with selected elements, which is used specifically for implementing mode 2 and 3.
• For mode 3, the core logic is finding those points which are only attached to one segment in all of the relevant segments, this approach also takes care of base cases like when there is a loop, etc.
• overlay_bezier_handles utility function is created to avoid repetition of code.

[Keavon]

!build

[github-actions]

📦 Build Complete for 5fae520
https://257d7226.graphite.pages.dev

[Keavon]

Marking as draft until the feedback I gave in the screencast sent on Discord is resolved.

[4adex]

Changes after first review -

• While in mode 2 or mode 3, when the new selection (on mouse down) has only anchors, then previous selection of points is stored in saved_points_before_handle_drag in tool_data
• In mode 3, if only one point is selected then behaviour is of mode 2.
• While dragging a handle you can also see the opposite handle.

[Keavon]

!build

[github-actions]

📦 Build Complete for 0e5e56c
https://ecd1b02b.graphite.pages.dev

[Keavon]

!build

[github-actions]

📦 Build Complete for 413e170
https://e79cfb71.graphite.pages.dev

[Keavon]

Here are four separate frontiers:

But the current implementation only treats 1 and 4 as frontiers, which means we don't see handles on either end of frontiers 2 and 3. We should see both handles around that unselected point, as a result.

[Keavon]

Another issue: in the Pen tool, when not drawing, all handles are shown regardless of mode.

[4adex]

will fix this asap in another PR