Fix Issue 20182 - [REG 2.086.0] std.traits.ParameterDefaults fails for copy constructor of nested struct

[RazvanN7]

The body of the mixin does a copy initialization of the parameter. However, the copy constructor cannot be used with context pointers. This is a known issue: https://issues.dlang.org/show_bug.cgi?id=22239 .

However, this PR solves the issue by implementing a workaround that also might be a potential optimization.

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	20182	regression	[REG 2.086.0] std.traits.ParameterDefaults fails for copy constructor of nested struct

⚠️⚠️⚠️ Warnings ⚠️⚠️⚠️

• Regression or critical bug fixes should always target the stable branch. Learn more about rebasing to stable or the D release process.

To target stable perform these two steps:

1. Rebase your branch to upstream/stable:

git rebase --onto upstream/stable upstream/master

2. Change the base branch of your PR to stable

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 + phobos#8433"

[dkorpel]

Is this targeting master again because it's related to other copy constructor fixes?

[thewilsonator]

I suspect its because its old.

[RazvanN7]

@dkorpel Yes.