[PATCH 0/6] fast-import: tighten parsing of paths

[Thalia Archibald <thalia@archibald.dev>]

fast-import has subtle differences in how it parses file paths between each
occurrence of <path> in the grammar. Many errors are suppressed or not checked,
which could lead to silent data corruption. A particularly bad case is when a
front-end sent escapes that Git doesn't recognize (e.g., hex escapes are not
supported), it would be treated as literal bytes instead of a quoted string.

Bring path parsing into line with the documented behavior and improve
documentation to fill in missing details.

This patch series is patterned after 06454cb9a3 (fast-import: tighten parsing of
datarefs, 2012-04-07), which did similar fixes across the grammar, but for
marks.

This is my first contribution to Git, so please let me know if there's something
I've missed. I'm working on a tool for advanced repo transformations (like a
union of filter-repo and Reposurgeon workflows), so I've been living in
fast-import code and I have more parsing fixes planned.

Thalia