Add extension packaging to build and test action

[mnoah1]

Update the github build and test action to include a packaging step.

• Updating package.json to include dependencies needed for packaging
• Updating vscodeignore, which is used to determine what gets included in the package. Most directories, especially node_modules, can be excluded as the extension.js already includes all packaged code, to keep extension size small.
• On each job run, the action will include a packaged extension artifact uploaded on the job run. Example: https://github.com/uber/vscode-bazel-bsp/actions/runs/9502950897

[shuklahy]

LGTM