fix: Project Settings UI update the absolute path

[wenytang-ms]

Summary

Fix Project Settings / Configure Classpath failing when adding a workspace-local JAR to a non-unmanaged Java project.

The UI previously converted selected JARs under the project root to project-relative paths. That is valid for unmanaged folders backed by java.project.referencedLibraries, but non-unmanaged projects apply library changes through JDT LS java.project.updateClassPaths, where CPE_LIBRARY entries must use absolute paths. Passing a relative path caused errors such as:

Path for IClasspathEntry must be absolute: lib/foo.jar

Changes

• Keep project-relative library paths only for unmanaged folders.
• Use absolute JAR paths when adding libraries for Maven/Gradle/Eclipse/other non-unmanaged projects.
• Add a defensive conversion before java.project.updateClassPaths so relative library entries are resolved against the project root before being sent to JDT LS.
• Extend the Java Extension Pack classpath autotest plan to cover adding a project-local JAR through the Project Settings Libraries UI and applying the classpath change.
• Add test case

Validation

• npm run compile
• node ../autotest/dist/cli/index.js validate ../vscode-java-pack/test-plans/java-extension-pack.yaml
• node ../autotest/dist/cli/index.js run test-plans/java-extension-pack.yaml --no-llm --output test-results/java-extension-pack-final

Fixes #1498
Related to microsoft/vscode-java-dependency#966

[Copilot]

Pull request overview

Updates the Project Settings Classpath UI messaging and path handling so library entries use the appropriate absolute/relative path format based on project type, and ensures classpath updates send absolute library paths when required by the backend workspace command.

Changes:

• Pass projectType from the webview when requesting the “Select Jar File” dialog.
• Emit absolute library paths for managed project types (Maven/Gradle/etc.), while keeping relative paths (when possible) for Unmanaged Folder projects.
• Convert relative library entries to absolute paths before invoking java.project.updateClassPaths.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/project-settings/handlers/ClasspathRequestHandler.ts	Uses projectType to decide whether to produce relative vs absolute library paths; normalizes relative library entries to absolute before updating classpaths.
src/project-settings/assets/vscode/utils.ts	Extends onWillSelectLibraries request payload to include projectType.
src/project-settings/assets/classpath/features/components/Libraries.tsx	Sends projectType when triggering the library selection flow.

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