[ddoc] Show TypeCtor method attributes after parameters

[ntrel]

This is more readable and avoids confusion when there's a non-void return type.

[dlang-bot]

Thanks for your pull request and interest in making D better, @ntrel! We are looking forward to reviewing it, and you should be hearing from a maintainer soon.
Please verify that your PR follows this checklist:

• My PR is fully covered with tests (you can see the coverage diff by visiting the details link of the codecov check)
• My PR is as minimal as possible (smaller, focused PRs are easier to review than big ones)
• I have provided a detailed rationale explaining my changes
• New or modified functions have Ddoc comments (with Params: and Returns:)

Please see CONTRIBUTING.md for more information.

---

If you have addressed all reviews or aren't sure how to proceed, don't hesitate to ping us with a simple comment.

Bugzilla references

Your PR doesn't reference any Bugzilla issue.

If your PR contains non-trivial changes, please reference a Bugzilla issue or create a manual changelog.

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + dmd#16708"

[ntrel]

buildkite failing due to ldc config issue:

CMake Error at cmake/Modules/FindLLVM.cmake:62 (message):
  Unsupported LLVM version 14.0.0 found (/bin/llvm-config).  At least version
  15.0 is required.  You can also set variables 'LLVM_ROOT_DIR' or
  'LLVM_CONFIG' to use a different LLVM installation.
Call Stack (most recent call first):
  cmake/Modules/FindLLVM.cmake:190 (_LLVM_FAIL)
  CMakeLists.txt:37 (find_package)

[dkorpel]

This is a great change, the immutable int f() {} syntax is easily confused with immutable(int) f() {}. Is there a reason to limit this to ddoc? Lots of error messages to update?

[ntrel]

I just thought the di change might be more disruptive, but yes it would be good. I might do that soon.