applets/manage-inputmethod: redesign, rework, fix

Reason for the change

Redesign the input method's applet to address several concerns and bug reports.

	Before	After
Click	Cycle show policy (never, touch, touch and mouse)	Show settings / Force show keyboard in hardware emulation mode if active client doesn't support text-input
Right-click	Context menu with button to access settings	Context menu with settings, as well as radio buttons to select show policy

Test plan

• Click the system tray applet to show settings
• With a client focused that doesn't support text-input (e.g. running under xwayland) click the applet to force show the OSK in hardware emulation mode
• Right-click the applet to switch modes and access settings

Screenshots or screen recordings

Icon

	Before	After
OSK Hidden
OSK Shown

Context menu

Before	After