Add Frame full screen support

[trypsynth]

Summary

• Adds wxd_Frame_ShowFullScreen and wxd_Frame_IsFullScreen, wrapping wxFrame's existing ShowFullScreen/IsFullScreen methods, the same pattern already used for Maximize/IsMaximized.
• Adds show_full_screen and is_full_screen methods to the Rust Frame wrapper.

Motivation

A downstream app needs full screen support for a document reading window, and this was missing from the Frame API.

Test plan

• cargo build -p wxdragon succeeds locally.