An example of how to create a C++ compilation database is needed

### Description of the problem / feature request:

Please provide a definitive example of how to create a [compilation database](https://clang.llvm.org/docs/JSONCompilationDatabase.html) for a Bazel-based C++ project.

### Feature requests: what underlying problem are you trying to solve with this feature?

There are numerous IDEs that rely on [clang language server](https://clangd.llvm.org/) (which requires compilation database for precise source indexing) to implement code browsing / code completion features for C++.

Start by reviewing Bazel's existing C++ documentation and the linked compilation database and clangd references. Add a definitive example for generating a compilation database in a Bazel-based C++ project, with enough context for IDE and language-server users to follow it. Done means the example is documented and can be followed successfully.

Written by the indexing model from the issue text.