[internal] Update to the latest @vscode/vsce for extension build

This isn't a logic change, but it fixes an npm warning during the
build. vsce itself hasn't had any major changes between 3.2.2 and 3.6.

* https://github.com/microsoft/vscode-vsce/releases/tag/v3.3.0
* https://github.com/microsoft/vscode-vsce/releases/tag/v3.4.0
* https://github.com/microsoft/vscode-vsce/releases/tag/v3.5.0
* https://github.com/microsoft/vscode-vsce/releases/tag/v3.6.0

Author: Wilfred