Adds a new "Import from Source..." menu item that opens a QScintilla
editor dialog where users can paste C/C++ struct definitions. The parser
tokenizes and parses the source using recursive descent, supporting
stdint.h types, Windows types (BYTE/DWORD/PVOID/etc), multi-word C
types, pointers, arrays, Vec2/3/4/Mat4x4 detection, unions (first
member), padding fields, typedefs, forward declarations, static_assert
size checks, and auto-detection of comment offset mode vs computed
offsets. Also removes the flaky test_editor cursor shape tests.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
