Fourslash: open all test files

[gabritto]

This PR makes fourslash open all test files upon initialization. This is needed because, in the absence of a tsconfig.json in the test files, the unopened files would not be part of the program.
In Strada we didn't have this problem with regular fourslash tests because fourslash would construct a program with all the test files explicitly. So now that we're running fourslash by calling the server, we need to open all the files so that they become part of an inferred project and thus part of the program we use for completions etc.

The base branch was changed.

[Copilot]

Pull Request Overview

This PR modifies fourslash tests to open all test files during initialization instead of just the first file. This ensures that all files are included in the language server program when a tsconfig.json is not present, fixing issues where unopened files would not be part of inferred projects and thus unavailable for language server operations like completions and find-all-references.

• Opens all test files during fourslash initialization
• Fixes test baseline files to show expected cross-file reference results
• Re-enables 4 JavaScript module tests that now pass with proper file opening

Reviewed Changes

Copilot reviewed 28 out of 28 changed files in this pull request and generated no comments.

File	Description
internal/fourslash/fourslash.go	Modified to open all test files instead of just the first one
internal/fourslash/_scripts/failingTests.txt	Removed 4 JavaScript module tests from failing list and added 2 JSDoc tests
Multiple baseline files	Updated to show proper cross-file reference results
Multiple test files	Removed t.Skip() calls to re-enable now-passing tests