Add CMake option C3_ENABLE_CLANGD_LSP (#1414)

* CMake option C3_ENABLE_CLANGD_LSP

The CMake option enables the generation of compile_commands.json in
the build directory and the creation of a symlink in the root
directory targeting the new file,
this will allow the Clangd Language Server Protocol (LSP) to
function properly.

* Added .editorconfig

EditorConfig helps maintain consistent coding styles:
https://editorconfig.org/

.gitignore

@@ -70,3 +70,8 @@ out/
 
 # Emacs files
 TAGS
+
+# Clangd LSP files
+/.cache/
+/compile_commands.json
+