build: Prepare 0.31.0 release

[wenytang-ms]

Summary

• Bump extension version from 0.30.5 to 0.31.0 in package.json and package-lock.json.
• Add 0.31.0 changelog covering the webview migration and Project Settings fix.

Validation

• npm run build

[Copilot]

Pull request overview

Prepares the vscode-java-pack extension pack for the 0.31.0 release by updating the published version metadata and documenting the release notes in the changelog.

Changes:

• Bump extension version from 0.30.5 to 0.31.0 in package.json.
• Align package-lock.json version fields to 0.31.0.
• Add a 0.31.0 entry to CHANGELOG.md summarizing key updates.

Reviewed changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated no comments.

File	Description
package.json	Updates the extension’s published version to 0.31.0.
package-lock.json	Updates lockfile version fields to match 0.31.0.
CHANGELOG.md	Adds release notes for 0.31.0 (webview migration + Project Settings fix).

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