Some cleanups to recovery.

- Remove the duplicate gCurrentUI variable in recovery.cpp;
- Refactor the load/save of locale functions;
- Clean up ui_print() to get rid of 256-byte buffer limit;
- Declare ui in common.h;
- Move the typedef of Volume into roots.h.

Test: Build and boot into recovery image.

Change-Id: Ia28c116858ca754133127a5ff9c722af67ad55b7

install.cpp

@@ -43,8 +43,6 @@
 #include "ui.h"
 #include "verifier.h"
 
-extern RecoveryUI* ui;
-
 #define ASSUMED_UPDATE_BINARY_NAME  "META-INF/com/google/android/update-binary"
 #define PUBLIC_KEYS_FILE "/res/keys"
 static constexpr const char* METADATA_PATH = "META-INF/com/android/metadata";