Fixes #5097. Kitty is wasting the keyboard shortcuts Ctrl+Shift+Alt+A/Z which returns as Ctrl+Alt+A/Z

[BDisp]

Fixes

• Fixes Kitty is wasting the keyboard shortcuts Ctrl+Shift+Alt+A/Z which returns as Ctrl+Alt+A/Z #5097

Proposed Changes/Todos

• Add Ctrl+Shift+Alt+A/Z combinations
• Fix AltGr+key printable keys combinations

Pull Request checklist:

• I've named my PR in the form of "Fixes #issue. Terse description."
• My code follows the style guidelines of Terminal.Gui - if you use Visual Studio, hit CTRL-K-D to automatically reformat your files before committing.
• My code follows the Terminal.Gui library design guidelines
• I ran dotnet test before commit
• I have made corresponding changes to the API documentation (using /// style comments)
• My changes generate no new warnings
• I have checked my code and corrected any poor grammar or misspellings
• I conducted basic QA to assure all features are working

[Copilot]

Pull request overview

This PR addresses kitty keyboard protocol parsing so modifier state (notably Ctrl+Shift+Alt) is preserved correctly, and adjusts text-input widgets to allow printable AltGr-generated characters while continuing to block most Alt/Ctrl-modified key insertions.

Changes:

• Preserve Ctrl+Shift+Alt modifier combinations when parsing kitty CSI u sequences.
• Allow TextField/TextView to insert printable AltGr combinations (via kitty associated text) while still rejecting most modified keys.
• Update Key shifted-printable rendering (AsGrapheme/AsRune) and expand/adjust kitty parsing tests.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
Tests/UnitTestsParallelizable/Views/TextViewTests.cs	Updates Alt+letter regression test setup/comments for kitty-associated-text behavior.
Tests/UnitTestsParallelizable/Views/TextFieldTests.cs	Updates Alt+letter regression test setup/comments for kitty-associated-text behavior.
Tests/UnitTestsParallelizable/Drivers/AnsiHandling/KittyKeyboardParsingTests.cs	Adjusts expectations for shifted printable keys and adds modifier/AltGr regression coverage.
Tests/UnitTestsParallelizable/Drivers/AnsiHandling/KittyAlternateKeyTests.cs	Updates end-to-end expectations for alternate keys with modifiers.
Terminal.Gui/Views/TextInput/TextView/TextView.Keyboard.cs	Allows printable AltGr (Alt+AssociatedText) insertion while blocking other modified keys.
Terminal.Gui/Views/TextInput/TextField/TextField.Keyboard.cs	Same AltGr insertion logic as TextView (with a small formatting issue).
Terminal.Gui/Input/Keyboard/Key.cs	Ensures shifted alternate keycodes produce correct grapheme/rune (esp. A–Z).
Terminal.Gui/Drivers/AnsiHandling/KittyKeyboardPattern.cs	Modifier-field handling changes and associated-text suppression tweaks for modified keys.