Rename indexed dbs with positron prefix

[sharon-wang]

• Addresses: Rename browser state IndexedDB database names #4864
• updates the prefixes for web IndexedDB databases and stores to use positron instead of vscode
• we don't delete the existing stores that are prefixed with vscode

I've done some testing on a dev build of Server Web on Mac and a local release build of Positron on Workbench on Ubuntu 24.

QA Notes

• this change impacts Positron Web / Server Web only
• the data stores are working if:
  • you're seeing the renamed databases and stores in Developer Tools > Application > Storage > IndexedDB
  • the layout state is being persisted when you close and reopen Positron in the same browser; for example:
    1. Open up a folder in Positron Web / Server Web
    2. Command Prompt > View: Toggle Zen Mode
    3. Close the browser
    4. Open up the same folder in the same browser in Positron Web / Server Web
    5. You should still be in Zen Mode