change SR to ScopeRef, make it global

[WalterBright]

Instead of repeating this logic (badly) move buildSR to being a global so other code can use it:

1. rename SR to ScopeRef to make it easily searchable
2. rename buildSR to buildScopeRef
3. move ScopeRef and buildScopeRef to module scope

[dlang-bot]

Thanks for your pull request, @WalterBright!

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 run digger -- build "master + dmd#12819"

[RazvanN7]

If you're not planning to use them in subsequent PRs, I suggest you make these declarations private.

[WalterBright]

but I am!

[RazvanN7]

The C++ headers need to be updated.

[ibuclaw]

Don't be alarmed! Attempting to clear the backlog - for context, all Azure/x86/OMF pipelines are broken and will hang for 2 hours, meanwhile possible fix will otherwise have to wait 6 hours or more until we know the result. Will re-open this in about 15-30 minutes.

[WalterBright]

Good! Thanks for your help with this.

[ibuclaw]

Good! Thanks for your help with this.

If you have any tips for fixing optlink, they would be welcome. See #12823 (comment)