Disable drag indicator for ineligible displays

An older change(I40b82ac54b58d8e58b7a87c8fe3c68cdda480e3c) was
implemented to disable the drag indicator for non-desktop-mode-supported
displays. But the fix was not comprehensive. This commit uses the
consolidated method in ShellDesktopState to verify a display's
eligibility as a drop target before showing the indicator.

Bug: b/383069176
Test: manual and atest
Flag: com.android.window.flags.enable_block_non_desktop_display_window_drag_bugfix
Change-Id: Iaad418172382e6c19845f83c3777ae0c28eb2284