Unify LLVM/Clang build jobs for Qt Creator and QDoc

Currently we have two LLVM/Clang builds jobs:

1. One for Qt Creator https://download.qt.io/development_releases/prebuilt/libclang/
2. One for QDoc https://download.qt.io/development_releases/prebuilt/libclang/qt/

The QDoc job needs a static build so that qdoc.exe will not have any external dependencies.

Since Qt Creator moved to clangd, it has less dependencies to LLVM/Clang libraries.

These two jobs can be now unified to have only one build.