MOVEONLY: Move IsBDBFile, IsSQLiteFile, and ListWalletDir

This commit does not change to any code and behavior. It it is easily reviewed
with the --color-moved=dimmed_zebra git diff option.

Motivation for this change is to:

- Consolidate redundant functions
  IsBDBFile /ExistsBerkeleyDatabase / SplitWalletPath, and
  IsSQLiteFile / ExistsSQLiteDatabase in the next commits

- Detect SQLite wallets consistently regardless whether bitcoin is built with
  SQLite support in the next commits

- Avoid attempting to open SQLite databases with the BDB library when bitcoin
  is built without SQLite support in the next commits

src/wallet/bdb.cpp

@@ -839,28 +839,3 @@ std::unique_ptr<BerkeleyDatabase> MakeBerkeleyDatabase(const fs::path& path, con
     status = DatabaseStatus::SUCCESS;
     return db;
 }
-
-bool IsBDBFile(const fs::path& path)
-{
-    if (!fs::exists(path)) return false;
-
-    // A Berkeley DB Btree file has at least 4K.
-    // This check also prevents opening lock files.
-    boost::system::error_code ec;
-    auto size = fs::file_size(path, ec);
-    if (ec) LogPrintf("%s: %s %s\n", __func__, ec.message(), path.string());
-    if (size < 4096) return false;
-
-    fsbridge::ifstream file(path, std::ios::binary);
-    if (!file.is_open()) return false;
-
-    file.seekg(12, std::ios::beg); // Magic bytes start at offset 12
-    uint32_t data = 0;
-    file.read((char*) &data, sizeof(data)); // Read 4 bytes of file to compare against magic
-
-    // Berkeley DB Btree magic bytes, from:
-    //  https://github.com/file/file/blob/5824af38469ec1ca9ac3ffd251e7afe9dc11e227/magic/Magdir/database#L74-L75
-    //  - big endian systems - 00 05 31 62
-    //  - little endian systems - 62 31 05 00
-    return data == 0x00053162 || data == 0x62310500;
-}