Convert to Uppercase and Convert to Lowercase commands in the code editor

The Studio code editor has Edit menu commands for toggling comments, duplicating and deleting lines, but no way to change the case of selected text. This adds two Edit menu commands to the code editor:

• Convert to Uppercase - Ctrl+Shift+U on Windows and Linux, Cmd+Shift+U on macOS
• Convert to Lowercase - Ctrl+U on Windows and Linux, Cmd+U on macOS

Both act on the current text selection and use the same shortcuts as Visual Studio. They are only available when the selection is non-empty. Typical use: fixing up mixed-case data pasted into string literals and keeping constants and comparisons visually consistent.