Add ability to consume ghosts when game is in frightened state

[nucleartide]

Challenge

In the classic game Pacman, Pacman is able to consume large "energizer" dots that temporarily switch the game into a "frightened" state:

test.mov

In this "frightened" state, ghosts move slowly in a randomized fashion. Pacman is also able to consume ghosts, after which their remaining eyes will double-time it back to the ghost house to be revived.

The goal of this pull request is to implement that behavior.

Changelog

• Ghost state. Introduce an EGhostState that is a per-AGhostAiController piece of state.
• Movement speeds. Customize movement speed when ghost is frightened, returning to ghost house, or navigating normally.
• Passable check. Refine “passable” check for determining whether a ghost can navigate to a tile.
• Overlap behavior. Pacman will eat a ghost if the ghost is frightened; Pacman will die if the ghost is not frightened.
• Ghost visuals. In an eaten state, the ghost’s head and body are invisible, and only the eyes are visible.
• Movement paths. Note that these are updated on state transitions as well as on path completion, as well as when the ghost is eaten (in order to plot a path back to the ghost house).
• Revival. Upon entering the ghost house, the ghost’s body reappears and the ghost returns to a normal movement pattern.

Dev checklist

• First draft. Implement a working first pass at the feature.
• First playtest. Thoroughly playtest until you are confident that the feature (and existing features) work.
• Final draft. Perform a general review of Files changed and revise anything that needs to be cleaned up.
• Final playtest. After the changes above, playtest through the game one last time to ensure that everything works.

Release checklist

• Fill out the pull request template. Self-explanatory.
• Remember the GIFs. Include a recording of what's going on!
• Merge and release. Merge into master, cut a new build in Unreal, and upload a release to Google Drive.
• Priorities. Prioritize items on work board.
• Next task. Tee up a pull request for the next feature.