Fourslash is broken when making requests in unconfigured .js files

Error message:
-

```
--- FAIL: TestAutoImportCompletionJs (0.07s)
c:/typescript-go/internal/fourslash/tests/autoImportCompletion_test.go:159: At marker 'd': textDocument/completion request returned error: [-32603]: no project found for URI file:///d.js
FAIL
FAIL github.com/microsoft/typescript-go/internal/fourslash/tests 1.758s
```

Repro:
-
Fails on requests called in .js files (formatting, completions, codefixes, etc)

Example: in `internal/fourslash/tests/autoImportCompletions_test.go`:
```
func TestAutoImportCompletionJs(t *testing.T) {
t.Parallel()
defer testutil.RecoverAndFail(t, "Panic on fourslash test")
const content = `// @Filename: a.js
export const someVar = 10;

// @Filename: d.js
import {someVar} from "./a";
someVar;
a/*d*/
`
f, done := fourslash.NewFourslash(t, nil /*capabilities*/, content)
defer done()
f.VerifyCompletions(t, "d", &fourslash.CompletionsExpectedList{
UserPreferences: &lsutil.UserPreferences{
IncludeCompletionsForModuleExports: core.TSTrue,
IncludeCompletionsForImportStatements: core.TSTrue,
},
IsIncomplete: false,
ItemDefaults: &fourslash.CompletionsExpectedItemDefaults{
CommitCharacters: &DefaultCommitCharacters,
EditRange: Ignored,
},
Items: &fourslash.CompletionsExpectedItems{
Includes: []fourslash.CompletionsExpectedItem{"someVar", "anotherVar"},
},
})
}
```

Info:
-
I've traced it back to .js files not being found in a project during `GetDefaultProject`