Terminal Switcher: Rename terminal should be populated and have selection

[kieferrm]

While testing #31784.

• VSCode Version: Code - Insiders 1.15.0-insider (f39385b, 2017-08-01T05:07:59.267Z)
• OS Version: Darwin x64 16.7.0

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Steps to Reproduce:

1. Open a terminal
2. Select Terminal: Switch Active Terminal from the command palette
3. ArrowDown to the terminal in the switcher
4. Move keyboard focus to rename action using 2 Tabs. See Terminal Switcher: Rename should be reachable with first tab #31835.
5. Enter to enter rename mode
   -> text box is empty. This is fine if I want to assign a completely new name, but an issue if I only want to correct a typo for example. The input box should contain the old name and the name should be selected so that I can start typing to replace or use Arrow keys to get to the right place to correct the typo.