feat: add debug commands for folder counts and files (#10206)

This adds two debugging commands that print information directly from
the database; one for folder counts, and one for file metadata for files
matching a pattern in a folder. E.g.,

```
% syncthing debug database-counts p3jms-73gps
DEVICE   TYPE       FLAGS    DELETED  COUNT  SIZE
-local-  FILE       -------  ---      0      0
-local-  FILE       --G----  ---      2473   70094796496
-local-  DIRECTORY  -------  ---      0      0
-local-  DIRECTORY  --G----  ---      19     2432
PSEUDOP  FILE       -------  ---      2473   70094796496
PSEUDOP  FILE       -nG----  ---      0      0
PSEUDOP  DIRECTORY  -------  ---      19     2432
PSEUDOP  DIRECTORY  -nG----  ---      0      0
```

```
% syncthing debug database-file p3jms-73gps 20240929-DSCF1387
DSCF1387
DEVICE   TYPE  NAME                          SEQUENCE  DELETED  MODIFIED                        SIZE      FLAGS    VERSION             BLOCKLIST
-local-  FILE  Austin/20240929-DSCF1387.raf  1204      ---      2024-09-29T01:10:54Z            48911888  --G----  HX2ELNU:1744213700  fsQdMvUL
PSEUDOP  FILE  Austin/20240929-DSCF1387.raf  22279     ---      2024-09-29T01:10:54Z            48911888  -------  HX2ELNU:1744213700  fsQdMvUL
-local-  FILE  Austin/20240929-DSCF1387.xmp  1196      ---      2024-10-16T08:08:35.137501751Z  5579      --G----  HX2ELNU:1744213700  xDGMnepi
PSEUDOP  FILE  Austin/20240929-DSCF1387.xmp  19910     ---      2024-10-16T08:08:35.137501751Z  5579      -------  HX2ELNU:1744213700  xDGMnepi
```

The local flag bits get a string representation for the bitmask,

```
	FlagLocalUnsupported:   "u",
	FlagLocalIgnored:       "i",
	FlagLocalMustRescan:    "r",
	FlagLocalReceiveOnly:   "e",
	FlagLocalGlobal:        "G",
	FlagLocalNeeded:        "n",
	FlagLocalRemoteInvalid: "v",
```

internal/db/sqlite/db_folderdb.go

@@ -10,6 +10,7 @@ import (
 	"database/sql"
 	"errors"
 	"fmt"
+	"io"
 	"iter"
 	"path/filepath"
 	"strings"
@@ -376,6 +377,22 @@ func (s *DB) DropDevice(device protocol.DeviceID) error {
 	})
 }
 
+func (s *DB) DebugCounts(out io.Writer, folder string) error {
+	fdb, err := s.getFolderDB(folder, false)
+	if err != nil {
+		return err
+	}
+	return fdb.DebugCounts(out)
+}
+
+func (s *DB) DebugFilePattern(out io.Writer, folder, name string) error {
+	fdb, err := s.getFolderDB(folder, false)
+	if err != nil {
+		return err
+	}
+	return fdb.DebugFilePattern(out, name)
+}
+
 // forEachFolder runs the function for each currently open folderDB,
 // returning the first error that was encountered.
 func (s *DB) forEachFolder(fn func(fdb *folderDB) error) error {