fallback for cursor grab mode during window creation

[mockersf]

Objective

• Fixes CursorGrabMode::Confined on Linux panicks on startup #7007
• do not panic when using an unsupported cursor grab mode

Solution

• Apply [Merged by Bors] - Fix set_cursor_grab_mode to try an alternative mode before giving an error #6599 also at window creation time
• Fallback to alternative method of cursor grab if the one selected is not available

[VitalyAnkh]

Fallback to alternative method of cursor grab if the one selected is not available

IMHO it's OK to set cursor grab mode to confined on X11 or Wayland platform. It crashes because we set it too early. Maybe you could look into my PR #7010?