Fix 22934 - Emit context pointer as outer instead of this

[MoonlightSentinel]

Because the latter is obviosly not a valid identifier.

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	22934	normal	Header generator emits context pointer as `this`

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#13887"

[MoonlightSentinel]

Fixed the typo in the commit title

[PetarKirov]

Can it be emitted as private?

[MoonlightSentinel]

Sure but why? The outer property isn't private in D.

[ljmf00]

This will break the dtoh end-user API. Probably we should add a changelog entry explaining it.

[MoonlightSentinel]

How so? Any header affected by this change wasn't compilable anyways (this is a reserved identifier)

Changelog added, also this fixes an emits invalid