extensionUtils: Add DISABLING and ENABLING extension states

Extensions can export asynchronous enable() and disable()
functions. To guard against re-entrancy when enabling or
disabling an extension, this commit adds two new states:
ENABLING and DISABLING which are set immediately prior
to calling enable() and disable() respectively.

This commit updates the extensions CLI and Extensions app
with new strings for these states.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2364>

subprojects/extensions-tool/src/common.h

@@ -36,6 +36,8 @@ typedef enum {
   STATE_OUT_OF_DATE,
   STATE_DOWNLOADING,
   STATE_INITIALIZED,
+  STATE_DISABLING,
+  STATE_ENABLING,
 
   STATE_UNINSTALLED = 99
 } ExtensionState;