Add native "Convert to UPPERCASE/lowercase" shortcut for selected text

### Description of the new feature / enhancement

Windows has no built-in way to convert selected text to UPPERCASE, lowercase, or Title Case across any application. Word has Shift+F3 for this, but it only works inside Word itself.

I'd like to see PowerToys add a global keyboard shortcut that converts the case of currently selected text anywhere in the OS (browser fields, chat apps, Notepad, etc.), similar to how Advanced Paste already handles clipboard transformations.

### Scenario when this would be used?

As a power user, I often write text in browsers, chat apps, or forms and later need to convert it to uppercase (e.g. for emphasis, headers, or formatting requirements). Right now the only workaround is copying the text into Word, applying Shift+F3, and pasting it back — which is slow and breaks my workflow. A native shortcut would save time for anyone who edits text daily across multiple apps.

### Supporting information

Advanced Paste in PowerToys already demonstrates that text transformation on paste is feasible. Extending this concept to a "transform selected text in place" shortcut would be a natural addition.

The issue identifies Advanced Paste as the closest existing precedent; start by tracing how it handles text transformations and user-configured shortcuts. Define the supported Windows applications and shortcut behavior, then verify that selected text can be transformed to uppercase, lowercase, and Title Case in those applications without breaking the surrounding workflow.

Written by the indexing model from the issue text.