Convert AssemblyChecker to use MetadataLoadContext to avoid file locking.

[jkoritzinsky]

The existing implementation was leading to file lock conflicts on #133188 and other managed ILASM PRs.

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[Copilot]

Copilot review overview

🟡 Changes recommended

The new MetadataLoadContext resolver strategy is likely to fail on assemblies with non-runtime attribute dependencies, and several thrown exceptions are missing actionable messages.

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Review tier: Lite
Findings: 2 · 1

New issues introduced by this change (3)

Severity	Finding
	src/​coreclr/​tools/​AssemblyChecker/​AssemblyInspector.cs — MetadataLoadContext resolution is currently limited to runtime assemblies, but IsDebug enumerates…
	src/​coreclr/​tools/​AssemblyChecker/​AssemblyInspector.cs — RuntimeAssemblyResolver currently relies on typeof(object).Assembly.Location to find the runtime…
	src/​coreclr/​tools/​AssemblyChecker/​AssemblyInspector.cs — Throwing BadImageFormatException without a message makes failures hard to diagnose. Include a brief…

What changed in this PR

This PR updates the CoreCLR AssemblyChecker tool’s --is-debug check by moving the implementation out of Program.cs into a new helper that uses MetadataLoadContext, aiming to avoid persistent file locks caused by Assembly.LoadFrom.

Changes:

• Removed the in-process Assembly.LoadFrom-based debug check from Program.cs and routed --is-debug through a new helper.
• Added AssemblyInspector.IsDebug using MetadataLoadContext to inspect DebuggableAttribute.
• Added a System.Reflection.MetadataLoadContext package reference to support the new implementation.

File	Description
src/​coreclr/​tools/​AssemblyChecker/​Program.cs	Removes the Assembly.LoadFrom-based IsDebug implementation and forwards --is-debug to AssemblyInspector.
src/​coreclr/​tools/​AssemblyChecker/​AssemblyInspector.cs	Adds MetadataLoadContext-based logic and a resolver to determine whether optimizations are disabled via DebuggableAttribute.
src/​coreclr/​tools/​AssemblyChecker/​AssemblyChecker.csproj	Adds the System.Reflection.MetadataLoadContext package dependency.

Suppressed comments (2)

src/coreclr/tools/AssemblyChecker/AssemblyInspector.cs:53

• Throwing BadImageFormatException without a message makes failures hard to diagnose. Include a brief message (and ideally the path) so consumers can tell which assembly/attribute was malformed.

                else
                {
                    throw new BadImageFormatException();
                }

src/coreclr/tools/AssemblyChecker/AssemblyInspector.cs:43

• Throwing BadImageFormatException without a message makes failures hard to diagnose. Include a brief message (and ideally the path) so consumers can tell which assembly/attribute was malformed.

                {
                    if (arguments[1].Value is not bool optimizationsDisabled)
                    {
                        throw new BadImageFormatException();
                    }