git storage: handle file renames between folders

[EricFromCanada]

I've discovered that my implementation of handling moved or renamed files for git storage in #4307 was incomplete. It turns out that if the old and new file paths have common elements, git diff --stat -M <hash-before> <hash-after> (called by this.git.diffSummary) will display them in a compressed format using braces. This commit updates the logic to handle all the non-renaming, simple renaming, and compressed renaming formats that I was able to find. Examples are below:

// edit top level file
file.md
// rename top level file
file.md => index.md
// move file to folder
index.md => folder/index.md
// rename folder, or move file between folders
{folder => directory}/index.md
// rename file in folder
directory/{index.md => subindex.md}
// move file to subfolder
directory/{ => subdir}/subindex.md
// rename subfolder, or move file between subfolders
directory/{subdir => subdirectory}/subindex.md
// move file from subfolder
directory/{subdirectory => }/subindex.md
// move and rename file to subfolder
directory/{subindex.md => subdirectory/sub-index.md}
// move and rename file between subfolders
directory/{subdirectory/sub-index.md => subdir/subdir-index.md}
// move and rename file from subfolder
directory/{subdir/subdir-index.md => dir-index.md}
// move and rename file between folders
directory/dir-index.md => other/other-index.md
// move and rename file to top level
other/other-index.md => home.md

This also updates the destinationTitle logic to better detect and update page titles that have not been updated since being auto-generated from the page's path, which originally worked only for top-level pages.

This should fix the behaviour observed in #4701 and potentially #4677.