Adventure mode actor collisions (update of #1037)

[jessemillar]

• Please check if the PR fulfills these requirements

• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

Feature

• What is the current behavior? (You can also link to an open issue here)

Adventure mode does not support solid collision between actors and the player.

• What is the new behavior (if this is a feature change)?

Actors have a 'solid' property. When it is enabled, the player will collide with other actors like a wall. Diagonal movement allows the player to slide along the edge of solid actors (even when the solid actor is moving).

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)

No breaking changes.

• Other information:

This PR is a modification of #1037. I solved the merge conflicts, implemented @chrismaltby's suggestion of increasing a check to + 3 and > 6, and fixed the bug reported in solid_bug2.mp4.

I did not tackle the Platforming bug report from solid_bug.mp4 in my PR because I haven't build a platforming game yet and currently have no need for the enhancements.

As an aside, when copying and pasting an actor with the new, solid direction checkboxes ("Top", "Bottom", etc.), the checkbox values are not properly copied after pasting. I perused the paste helpers and middleware but could not figure out how to add support. I'd be happy to if someone more knowledgeable could give me a tip.

This is a test GB Studio project that I used to verify functionality.
collision-tests-clean-merge.zip