Move _d_arraysetlengthT* into a template to always instantiate both

[Vild]

This PR fixes two problem that happens when trying to apply dlang/dmd#10106.

Firstly, it marks the hooks with pragma(inline, false) to not break the dmd/dinterpret.d ctfe interception code.

Secondly, it wraps both of the hooks inside of a template to force the compiler to create an instance of both function for every type that is used.
This fixes a undefined reference problem that can will happen when Appender from phobos is used with -profile=gc. The linker complains about a missing _d_arraysetlengthTTrace!Tarr instance, as phobos only had the _d_arraysetlengthT!Tarr instance compiled in its library, and not the _d_arraysetlengthTTrace!Tarr instance. By forcing both hooks to be always be instantiated, this problem will not happen.

[dlang-bot]

Thanks for your pull request and interest in making D better, @Vild! 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 fetch digger
dub run digger -- build "master + druntime#2667"