swift-testing: If LSP is disabled, swift-testing tests do not work

[adam-fowler]

It appears swift-testing tests are not flagged as swift-testing until they are found via the workspace/tests or textDocument/tests LSP requests. We need another way to catch this. While disabling SourceKit-LSP is a special situation, it could occur in situations where LSP is particularly slow in large projects.

[award999]

Swift-testing is more complex than XCTests so Paul said he would be hesitant to parse this. Some ideas:

1. Update setting description, warning if they disable sourcekit-lsp, they lose this functionality
2. Update warning notification message that shows up to kill the LSP
3. Provide warning in testing view (if we can still show XCTests at same time)