chore: stop treating dirs as having size 128 (#10750)

Resp. directories for the database, and both dirs and symlinks for
`FileInfo.FileSize`. Instead handle it in the UI progress percentage. We
even already have special cases there for deletions, might as well
handle directories just like any other zero-sized needed item there.

This went through the very thorough testing of running it on my laptop,
the migration was applied and it seemed to be working fine after.

---------

Signed-off-by: Simon Frei <freisim93@gmail.com>

lib/api/api.go

@@ -1774,7 +1774,7 @@ func fileIntfJSONMap(f protocol.FileInfo) map[string]interface{} {
 	out := map[string]interface{}{
 		"name":               f.FileName(),
 		"type":               f.FileType().String(),
-		"size":               f.FileSize(),
+		"size":               f.Size,
 		"deleted":            f.IsDeleted(),
 		"invalid":            f.IsInvalid(),
 		"ignored":            f.IsIgnored(),