Move toParentDecl to toParentLocal and make a new toParentDecl() which follows the declaration scope even for static templates

[SSoulaimane]

This is the correct behavior.
Includes a test case.

Edit: some code such as test/compilable/b16483.d and some tests I added relied on the old behavior so I kept it with another variant called toParentLocal() which doesn't follow non-local (i.e. global and static) templates. toParentLocal is even more useful when two local contexts exist (#9282).

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	6541	normal	using synchronized on a templated method crashes the compiler

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 + dmd#9647"

[jacob-carlborg]

Is this fixing some issue? In that case please create a bugzilla issue and reference so it show up in the changelog.

[SSoulaimane]

Is this fixing some issue? In that case please create a bugzilla issue and reference so it show up in the changelog.

Yes it is. Added.

[SSoulaimane]

Since some code relies on the current behavior I kept it under a different nametoParentLocal. this toParentLocal was coming anyway with #9282.