Add native modifier hotkey chords

[breno77alves]

Summary

• add native Ctrl/Alt/Shift/Meta + primary-key chords
• support chords for costumes, per-layer visibility toggles, and animation triggers
• keep existing single-key bindings compatible
• trigger bindings only on the primary-key edge, preventing repeats and accidental plain-key activation when a modifier is released
• ignore the legacy duplicate root godot-ndi copy; addons/godot-ndi remains the canonical plugin

Behavior

• modifier matching is exact (2 and Shift+2 are distinct)
• unrelated held gameplay keys such as W do not block a chord
• modifier-only input waits for a primary key during binding capture
• no external hotkey utility, driver, or dependency is used

Tests

• Godot 4.6.1 --headless --path test --script hotkey_binding_test.gd
• Windows project pack export with exactly one NDI extension in the generated extension list
• portable Windows launch: process remained running and responsive
• git diff upstream/main...HEAD --check

The optional NDI feature still requires the NDI 6.2 Runtime on the user's system. Missing NDI is reported by Godot but does not prevent the core application from starting.