Update GC interface to contain array management functions.

[schveiguy]

This migrates array management primitives into the GC. Each of these functions either updates the array used space, gets the array used space, or expands an array in-place in a GC-sanctioned way.

The intent is for the array runtime to defer to the GC for these operations, and allow innovation in these areas.

The primitives will never reallocate a block in order to expand it. That must be handled via a separate call to allocation routines (currently done in the lifetime module).

I purposely did not add these to core.memory yet, as these are only useful for internal operations managing array memory. This may remain that way, or in the future, we may expose this. For now, it's an internal detail, only relevant to GC implementors.

This was split into 2 commits The first migrates all the array functions from rt.lifetime to the conservative GC. The second commit fixes issues that were found during build/test. The 2 commits will help review actual changes to the code.

[dlang-bot]

Thanks for your pull request, @schveiguy!

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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#20608"

[schveiguy]

@Herringway any more comments on this? Please read the note about the trusted code.

[Herringway]

@Herringway any more comments on this? Please read the note about the trusted code.

I'm not really satisfied, but I'm not a GC expert in any sense and don't want to delay things further.