bug#69657: Missing imenu entries with eglot

[Felician Nemeth <felician.nemeth@gmail.com>]

> 1. Put this code in a C++ source file, e.g., test.cpp:
>
>    class Foo {
>      void bar() {}
>    };
>
> 2. Start eglot with clangd.
> 3. Invoke imenu; there will be a single entry "bar", nested under "Foo".
>    In particular, there is no entry that lets you jump to Foo.

How do you invoke imenu?  If I type M-x imenu-add-menubar-index RET,
then I cannot select "Foo" as you wrote above.  However, if I apply the
patch, the menu looks exactly the same.  On the other hand, the patch
seems to ruin breadcrumb-mode: putting the point after "{}", the
breadcrumb header line shows: "dir/test.cpp: Class > Foo" instead of the
original "dir/test.cpp: Class > Foo > bar".

$ clangd --version
Debian clangd version 14.0.6
Features: linux+grpc