Enable loading COM component in default ALC via runtime config setting

[elinor-fung]

Allow COM components to opt-in to being loaded in the default ALC:

• comhost checks for the System.Runtime.InteropServices.COM.LoadComponentInDefaultContext property and uses new functions on ComActivator, loading into the default context if the property is set to true
• Default behaviour remains loading into an isolated context
• Fall back to using ComActivator functions that always load into an isolated context if new functions aren't found and loading in an isolated context
  • For .NET 8, we shouldn't actually need to do this, but if we want to try backporting we would.

Resolves #66013

cc @AaronRobinsonMSFT

[ghost]

Tagging subscribers to this area: @vitek-karas, @agocke, @VSadov
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Issue Details

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Allow COM components to opt-in to being loaded in the default ALC:

• comhost checks for the System.Runtime.InteropServices.COM.LoadComponentInDefaultContext property and uses new functions on ComActivator, loading into the default context if the property is set to true
• Default behaviour remains loading into an isolated context
• Fall back to using ComActivator functions that always load into an isolated context if new functions aren't found and loading in an isolated context
  • For .NET 8, we shouldn't actually need to do this, but if we want to try backporting we would.

cc @AaronRobinsonMSFT

Author:	elinor-fung
Assignees:	-
Labels:	area-Host
Milestone:	-

[vitek-karas]

I like this approach.

Are we going to require people to use RuntimeHostConfigurationOption to specify the new property or do you think we should introduce a new property? (I'm split on this myself)

[elinor-fung]

Are we going to require people to use RuntimeHostConfigurationOption to specify the new property or do you think we should introduce a new property? (I'm split on this myself)

I was planning on just going with RuntimeHostConfigurationOption (and will update our COM sample to show it). It seems a bit too specific to me for a first-class property.

[elinor-fung]

Failure is #78778

[elinor-fung]

/backport to release/7.0-staging

[github-actions]

Started backporting to release/7.0-staging: https://github.com/dotnet/runtime/actions/runs/4623484015

[elinor-fung]

/backport to release/6.0-staging

[github-actions]

Started backporting to release/6.0-staging: https://github.com/dotnet/runtime/actions/runs/4623491666

[github-actions]

@elinor-fung backporting to release/7.0-staging failed, the patch most likely resulted in conflicts:

$ git am --3way --ignore-whitespace --keep-non-patch changes.patch

Applying: Enable loading COM component in default ALC via runtime config setting
Using index info to reconstruct a base tree...
M	src/coreclr/System.Private.CoreLib/src/Internal/Runtime/InteropServices/ComActivationContextInternal.cs
M	src/coreclr/System.Private.CoreLib/src/Internal/Runtime/InteropServices/ComActivator.cs
M	src/libraries/System.Private.CoreLib/src/ILLink/ILLink.Descriptors.LibraryBuild.xml
Falling back to patching base and 3-way merge...
Auto-merging src/libraries/System.Private.CoreLib/src/ILLink/ILLink.Descriptors.LibraryBuild.xml
CONFLICT (content): Merge conflict in src/libraries/System.Private.CoreLib/src/ILLink/ILLink.Descriptors.LibraryBuild.xml
Auto-merging src/coreclr/System.Private.CoreLib/src/Internal/Runtime/InteropServices/ComActivator.cs
Auto-merging src/coreclr/System.Private.CoreLib/src/Internal/Runtime/InteropServices/ComActivationContextInternal.cs
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
Patch failed at 0001 Enable loading COM component in default ALC via runtime config setting
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".
Error: The process '/usr/bin/git' failed with exit code 128

Please backport manually!

[github-actions]

@elinor-fung an error occurred while backporting to release/7.0-staging, please check the run log for details!

Error: git am failed, most likely due to a merge conflict.