build: prepare 0.31.1 patch release

[wenytang-ms]

Summary

• Bump the extension version to 0.31.1.
• Add the 0.31.1 changelog entry for notable fixes merged after 0.31.0, including webview CSP, Project Settings dropdown updates, and Java Help Center codicon font bundling.

Validation

• npx @vscode/vsce@latest package -o vscode-java-pack-0.31.1-verify.vsix
• Inspected the generated VSIX and confirmed version 0.31.1.
• Confirmed the VSIX contains no extension/test-fixtures/, extension/test-plans/, extension/test-results/, or JUnit entries.

[Copilot]

Pull request overview

Prepares the vscode-java-pack extension for the 0.31.1 patch release by updating the published version metadata and documenting the notable fixes included in the release.

Changes:

• Bump extension version from 0.31.0 to 0.31.1 in package.json.
• Sync package-lock.json version fields to 0.31.1.
• Add a 0.31.1 entry to CHANGELOG.md referencing the included fixes/PRs.

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 manifest version to 0.31.1.
package-lock.json	Aligns lockfile/package metadata version to 0.31.1.
CHANGELOG.md	Adds release notes for 0.31.1 with links to merged PRs.

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