VSCodium/clangd: Add generation of .clangd and .vscode files to ease editing via IDE/language-server

[sgothel]

Is your feature request related to a problem?

To allow a fast forward utilization of clang language server IDE's like VSCodium, I like our build system to generate required support files.

Goal is to allow easy editing including full clangd support, e.g. formatting, includes, tidy, refactor.

It is not a goal to support building nor debugging.

Describe the solution you'd like

Our build system, i.e. Makefile.am, should have rules to generate useful support files, e.g.

• compile_commands.json
  • already supported via make compile_commands
• .clangd
  • in addition to compile_commands.json, allowing setting include defaults and workspace-dir as well as other clangd settings
• .vscode/settings.json
  • VSCodium workspace settings
• .vscode/online.code-workspace
  • VSCodium workspace project file

A simple make gen-vscode should ensure generation of the above files, to launch a clang language server IDE, here VSCodium.

Eclipse CDT-LSP might be also of interest here.

This is similar to LibreOffice's vscode-ide-integration make target.