Allow disabling runtime versions via an environment variable

[elinor-fung]

Allow disabling specific runtime versions during framework resolution via an environment variable

• Read the DOTNET_DISABLE_RUNTIME_VERSIONS environment variable as one or more versions separated by semi-colons - for example, 9.0.7 or 9.0.2;9.0.7
  • Must be the exact version string. An invalid or non-existent version has no effect.
  • Resolver reads and stores this when it is created
• Update the framework resolution logic to skip disabled versions when searching for compatible frameworks
  • If all matching versions are disabled, resolution fails

Resolves #118553

cc @dotnet/appmodel @AaronRobinsonMSFT

[dotnet-policy-service]

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[Copilot]

Pull Request Overview

This PR implements functionality to allow disabling specific runtime versions during framework resolution via the DOTNET_DISABLE_RUNTIME_VERSIONS environment variable. The feature enables users to prevent the framework resolver from selecting specified versions, even if they would normally be chosen through roll-forward logic.

Key changes:

• Added environment variable parsing for semicolon-separated disabled versions
• Modified framework resolution logic to skip disabled versions during search
• Added comprehensive test coverage for various disable scenarios

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
src/native/corehost/fxr/fx_resolver.h	Moved constructor to implementation file and added member variable for disabled versions
src/native/corehost/fxr/fx_resolver.cpp	Implemented environment variable parsing, constructor, and disabled version checking in resolution logic
src/installer/tests/TestUtils/Constants.cs	Added constant for the new environment variable name
src/installer/tests/HostActivation.Tests/FrameworkResolution/FrameworkResolution.cs	Added comprehensive test cases covering single/multiple disabled versions and roll-forward scenarios

[elinor-fung]

/backport to release/10.0

[github-actions]

Started backporting to release/10.0: https://github.com/dotnet/runtime/actions/runs/17601140737

[github-actions]

@elinor-fung backporting to "release/10.0" failed, the patch most likely resulted in conflicts:

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

Applying: Allow disabling runtime versions via an environment variable
Applying: Update get_all_framework_infos, add test cases
.git/rebase-apply/patch:35: trailing whitespace.
            { 
warning: 1 line adds whitespace errors.
Using index info to reconstruct a base tree...
M	src/installer/tests/HostActivation.Tests/NativeHostApis.cs
Falling back to patching base and 3-way merge...
Auto-merging src/installer/tests/HostActivation.Tests/NativeHostApis.cs
CONFLICT (content): Merge conflict in src/installer/tests/HostActivation.Tests/NativeHostApis.cs
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
hint: When you have resolved this problem, run "git am --continue".
hint: If you prefer to skip this patch, run "git am --skip" instead.
hint: To restore the original branch and stop patching, run "git am --abort".
hint: Disable this message with "git config set advice.mergeConflict false"
Patch failed at 0002 Update get_all_framework_infos, add test cases
Error: The process '/usr/bin/git' failed with exit code 128

Please backport manually!