feat: add syncthing debug database-statistics command (#10117)

This adds a command that shows database statistics. Currently it
requires a fork of the sqlite package to add the dbstats virtual table;
the modernc variant already has it.

This also provides the canonical mapping between folder ID and database
file, for tinkerers...

```
% ./bin/syncthing debug database-statistics
DATABASE                 FOLDER ID    TABLE                                  SIZE     FILL
========                 ====== ==    =====                                  ====     ====
main.db                  -            folders                               4 KiB    8.4 %
main.db                  -            folders_database_name                 4 KiB    6.0 %
main.db                  -            kv                                    4 KiB   41.1 %
main.db                  -            schemamigrations                      4 KiB    3.9 %
main.db                  -            sqlite_autoindex_folders_1            4 KiB    3.7 %
...
folder.0007-txpxsvyd.db  w3ejt-fn4dm  indexids                              4 KiB    1.5 %
folder.0007-txpxsvyd.db  w3ejt-fn4dm  kv                                    4 KiB    0.8 %
folder.0007-txpxsvyd.db  w3ejt-fn4dm  mtimes                              608 KiB   81.5 %
folder.0007-txpxsvyd.db  w3ejt-fn4dm  schemamigrations                      4 KiB    3.9 %
folder.0007-txpxsvyd.db  w3ejt-fn4dm  sqlite_autoindex_blocklists_1      4108 KiB   89.5 %
folder.0007-txpxsvyd.db  w3ejt-fn4dm  sqlite_autoindex_blocks_1        700020 KiB   88.1 %
folder.0007-txpxsvyd.db  w3ejt-fn4dm  sqlite_autoindex_devices_1            4 KiB    3.6 %
folder.0007-txpxsvyd.db  w3ejt-fn4dm  sqlite_autoindex_kv_1                 4 KiB    0.6 %
folder.0007-txpxsvyd.db  w3ejt-fn4dm  sqlite_schema                        12 KiB   45.9 %
folder.0007-txpxsvyd.db  w3ejt-fn4dm  sqlite_sequence                       4 KiB    1.0 %
folder.0007-txpxsvyd.db  w3ejt-fn4dm  sqlite_stat1                          4 KiB   12.2 %
folder.0007-txpxsvyd.db  w3ejt-fn4dm  sqlite_stat4                          4 KiB    0.2 %
folder.0007-txpxsvyd.db  w3ejt-fn4dm  (total)                         1906020 KiB   92.8 %
main.db + children       -            (total)                         2205888 KiB   92.0 %
```

.github/workflows/build-syncthing.yaml

@@ -22,7 +22,7 @@ env:
   BUILD_USER: builder
   BUILD_HOST: github.syncthing.net
 
-  TAGS: "netgo osusergo sqlite_omit_load_extension"
+  TAGS: "netgo osusergo sqlite_omit_load_extension sqlite_dbstat"
 
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