Correctness and performance update to "diff --color-moved" feature.
* pw/diff-color-moved-fix:
diff --color-moved: intern strings
diff: use designated initializers for emitted_diff_symbol
diff --color-moved-ws=allow-indentation-change: improve hash lookups
diff --color-moved: stop clearing potential moved blocks
diff --color-moved: shrink potential moved blocks as we go
diff --color-moved: unify moved block growth functions
diff --color-moved: call comparison function directly
diff --color-moved-ws=allow-indentation-change: simplify and optimize
diff: simplify allow-indentation-change delta calculation
diff --color-moved: avoid false short line matches and bad zebra coloring
diff --color-moved=zebra: fix alternate coloring
diff --color-moved: rewind when discarding pmb
diff --color-moved: factor out function
diff --color-moved: clear all flags on blocks that are too short
diff --color-moved: add perf tests