Exclude autotest artifacts from VSIX package

The VSIX package was unintentionally including E2E test plans, fixtures, and local test results. Exclude those directories so test-only Maven fixtures and generated screenshots are not distributed with the extension.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: wenytang-ms

.vscodeignore

@@ -15,3 +15,6 @@ out/**/*.map
 *.vsix
 scripts
 .azure-pipelines/**
+test-fixtures/**
+test-plans/**
+test-results/**