[lldb-dap] bundle lldb-dap extension using esbuild (#160598)
The most recent version of the lldb-dap VS Code extension (0.2.17) fails
to activate because it's missing the `chokidar` dependency in the
`.vsix`. In order to prevent this from happening in the future, this PR
adds a `bundle-extension` step to extension packaging in order to bundle
the extension into a single `.js` file using esbuild. All dependencies
will be included in this bundle so that the `.vscodeignore` doesn't need
to be updated.