Battery for Text Diffing

[wmccrthy]

Adds a diffText battery, that implements a myers-diff esque algorithm using the notion of an edit graph. An edit graph is can be described as:

• src string along x axis
• destination string along y axis
• each edge in the graph represents a diff operation:
  • (n, n) -> (n+1, n) represents a deletion of src[n+1]
  • (n, n) -> (n, n+1) represents an addition of destination[n+1]
  • (n, n) -> (n+1, n+1) exists only if src[n+1] == destination[n+1]
• The shortest path from (0, 0) -> (len(src), len(destination)) represents the shortest-edit-sequence.

Myers-diff works by greedily following diagonal edges (n,n -> n+1,n+1) but the algorithm is not super intuitive / readable imo.

This implementation stays consistent with the greedy nature but varies slightly in how the graph is traversed. We use a deque to BFS the edit graph in a greedy fashion: whenever a node has a diagonal edge, we push it to the front of the deque, while other edges are always pushed to the back.

I included the deque implementation as a separate battery, since I figure it could provide other use down the line.

Both diffText and deque have solid test coverage.

Here is what the output of examples/diffText.luau looks like: