Chat customization: MCP page improvements

Testing #335626

- clone 'https://github.com/aeschli/vscode-customization-migration-test', open folder
- go to the MCP servers tab

1. Note the different fonts in 'Installed' and 'Available'

2. I don't like the scrollable section inside the collapsible tree. It's IMO it would be better if is just like a tree (always show all children)

3. Double scrollbars in Available

Maybe have the 'Available' section on a separate page, with a search bar?

4. To many state representations
- there is the running batch
- the checkbox (hover says 'Running')
- the slider (hover says 'Disable slack-vscode')
- the context menu has many more variants of disabling
- but how can uninstall it?

5. servers are not sorted by name