decouple rh vsc ext tester

[albertli-msft]

• Create a new private workspace project vscode-extension-tester/locators: a bunch of selectors to locate element in vsc by versions
• Create a new private workspace project vscode-extension-tester/page-objects: a bunch of wrapped utils to act certain functionality in vsc
• remove vsc-extension-tester dependency

if we liked this pattern, we could continue hardening the quality of the e2e test cases:

• Enrich locators/page-object libs
• Replace the await timeout in our previous await timeout
  Then it could stabilize the e2e test cases success rates. 😬