Directory rename detection testcases and rules

While testing merge-ort on some real world repositories a little while back, I found some issues with directory rename detection...some of which were issues in the current merge-recursive as well. Also, I found that there was a nice optimization I could use if a new obvious-looking rule was added, though it has one slight side effect to one corner case. Fixing the bugs and implementing the new rules is a bit more involved, so for now this series just updates the rule descriptions and adds or modifies tests to document the various cases.

Elijah Newren (4):
directory-rename-detection.txt: update references to regression tests
t6423: more involved directory rename test
t6423: update directory rename detection tests with new rule
t6423: more involved rules for renaming directories into each other

 .../technical/directory-rename-detection.txt  |  15 +-
 t/t6423-merge-rename-directories.sh           | 592 ++++++++++++++++--
 2 files changed, 553 insertions(+), 54 deletions(-)

base-commit: d4a392452e292ff924e79ec8458611c0f679d6d4
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-879%2Fnewren%2Fdrd-testcases-and-rules-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-879/newren/drd-testcases-and-rules-v1
Pull-Request: https://github.com/git/git/pull/879

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