Better C++ completion

[A2va]

• Use cpptools API for autocompletion without setting a compile_commands.json in c_cpp_properties.json
• Same for clangd, waiting to develop the API.

• cpptools
• clangd
• Update Intellisense when a file is created, even if there is globbing in the xmake.lua

• Could be implemented with xmake explorer, or with a file watcher. I'm not sure which is the best, the first one is definitely simpler.

Reference:
cmake-tools API example
cpptools npm package