Add diagnostics code and URL columns to problems view and markers view

I'd like to make diagnostics details like a problem marker's problem identifier (code) and a URL to the detailed problem description visible / accessible in the problems view and in the markers view.

As soon as the issue https://github.com/eclipse-platform/eclipse.platform.ui/issues/2193 is fixed, we should adapt LSP4E to use marker content generator extensions to add new marker fields "Code" and "Details URL" to the existing problems view and to the markers view. A user will then be able to show or hide each of these marker fields in the views based on her demands. Language server providers like CDT LSP will then be able to add diagnostics details, for example, from clang-tidy like readability-magic-numbers and https://clang.llvm.org/extra/clang-tidy/checks/readability/magic-numbers.html.

This feature request is related to issue #185 and PR #1066.

Review the dependency issue #2193, then inspect the existing problems view and markers view integration and the marker content generator extension approach described in the issue. Use related issue #185 and PR #1066 for context. Done means both views expose optional Code and Details URL fields that language server providers can populate.