[stable34] fix(files_sharing): normalize share target on parent folder rename - #64143

When a recipient moved an incoming share into one of their own folders
and later renamed that folder, Updater::renameChildren passed the mount
point to SharedMount::moveMount. Mount points always end in a slash, and
stripUserFilesPath did not normalize its result, so the slash was stored
in share.file_target. PROPFIND on such a share then returns 500.
Normalize the stripped path so no caller can write a trailing slash, and
repair rows that are already affected.
Signed-off-by: silver <s.szmajduch@posteo.de>
Assisted-by: ClaudeCode:claude-opus-5

Signed-off-by: Ferdinand Thiessen <opensource@fthiessen.de>

perf(core): only run the trailing slash share repair once
Signed-off-by: silver <s.szmajduch@posteo.de>
Assisted-by: ClaudeCode:claude-opus-5
[skip ci]

Signed-off-by: silver <s.szmajduch@posteo.de>