Document clangd update procedure

Arduino IDE has dependencies on the clangd C++ language server and ClangFormat code formatter tools. These are updated
periodically to benefit from the ongoing development on those projects.

The update procedure requires operations in three different repositories:

- Generate builds in arduino/clang-static-binaries
- Validate and update formatter configuration in arduino/tooling-project-assets
- Update metadata in arduino/arduino-ide

Previously, this was undocumented and the procedure existed only in the form of "institutional memory".

The procedure is now fully documented in the readme of arduino-ide-extension.

Author: per1234

Diff for: arduino-ide-extension/README.md

@@ -62,6 +62,15 @@ The Config Service knows about your system, like for example the default sketch
   - Some CLI updates can bring changes to the gRPC interfaces, as the API might change. gRPC interfaces can be updated running the command
     `yarn --cwd arduino-ide-extension generate-protocol`
 
+### Update **clangd** and **ClangFormat**
+
+The [**clangd** C++ language server](https://clangd.llvm.org/) and the [**ClangFormat** code formatter](https://clang.llvm.org/docs/ClangFormat.html) tool dependencies are managed in parallel. Updating them to a different version is done by the following procedure:
+
+1. If the target version is not already [available from the `arduino/clang-static-binaries` repository](https://github.com/arduino/clang-static-binaries/releases), submit [an issue there](https://github.com/arduino/clang-static-binaries/issues) requesting a build and wait for that to be completed.
+1. Validate the **ClangFormat** configuration for the target version by following the instructions [**here**](https://github.com/arduino/tooling-project-assets/tree/main/other/clang-format-configuration#clangformat-version-updates)
+1. Submit a pull request in the `arduino/arduino-ide` repository to update the version in the `arduino.clangd.version` key of [`package.json`](package.json).
+1. Submit a pull request in [the `arduino/tooling-project-assets` repository](https://github.com/arduino/tooling-project-assets) to update the version in the `vars.DEFAULT_CLANG_FORMAT_VERSION` field of [`Taskfile.yml`](https://github.com/arduino/tooling-project-assets/blob/main/Taskfile.yml).
+
 ### Customize Icons
 ArduinoIde uses a customized version of FontAwesome.
 In order to update/replace icons follow the following steps: