Fix error baselines for empty files

[jakebailey]

The old code said:

        const dupeCase = new Map<string, number>();
        for (const inputFile of inputFiles.filter(f => f.content !== undefined)) {
            // Filter down to the errors in the file

Except, content is string and could never be undefined; tests in Strada pass without the filter!

The ported code instead did a length check, which threw away files that should have been baselined. Just remove that filter.

For https://github.com/microsoft/typescript-go/pull/1013/files/35b83e8d784ce2679e1b377dd80dab9f412f3d97#r2121715758

[Copilot]

Pull Request Overview

This PR fixes error baseline generation by removing an unnecessary filter that skipped files with empty content.

• Removed filtering of input files based on content length in error_baseline.go.
• Updated baseline error files to reflect the expected output without the filter.

Reviewed Changes

Copilot reviewed 23 out of 23 changed files in this pull request and generated 1 comment.

File	Description
internal/testutil/tsbaseline/error_baseline.go	Removed the non-empty file filter to process all input files, including those with empty content.
testdata/baselines/reference/*	Updated baseline files to match the new error baseline outputs.