feat: Add a "Preview" Tab to the KMD KPS "Description" Window

### Is your feature request related to a problem? Please describe.

When composing and editing Markdown text in the `Description` field, it requires extra steps, outside of KMD, to know how the rendered text will appear. This adds a little extra time and inconvenience to the developer.

### Describe the solution you'd like

Following the GitHub UI model, a tab, with label "Preview" could be added to the top of the `Description` window that when clicked would present the interpreted and rendered Markdown text. The window size should also be stretchable.

### Describe alternatives you've considered

Copying and pasting the text into an external `.md` file to produce a preview in another tool.

### Related issues

_No response_

### Keyman apps

- [ ] Keyman for Android
- [ ] Keyman for iPhone and iPad
- [ ] Keyman for Linux
- [ ] Keyman for macOS
- [ ] Keyman for Windows
- [x] Keyman Developer
- [ ] KeymanWeb
- [ ] Other - give details at bottom of form

### Keyman version

Current Release

### Operating system

Windows 11

### Device

N/A

### Target application

N/A

### Browser

N/A

### Keyboard name

N/A

### Keyboard version

N/A

### Language name

N/A

### Additional context

_No response_