[cDAC] Implement IsValidObject for cDAC

[barosiak]

Summary

Implement IsValidObject in the cDAC.

Changes

• Implemented DacDbiImpl.IsValidObject
• Added ContinuationSingletonEEClass global pointer to datadescriptor.inc
• Added GetClassPointer, IsCanonicalMethodTable, IsContinuationWithoutMetadata APIs to the IRuntimeTypeSystem contract and RuntimeTypeSystem_1APIs to the IRuntimeTypeSystem contract and RuntimeTypeSystem_1
• Added parameterized tests for the new APIs

Note to copilot code review: we don't care about compat with older dumps or runtimes or api review

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[Copilot]

Pull request overview

This PR extends the cDAC runtime type system contract (and its tests/mocks) to support additional MethodTable/EEClass queries, then uses those APIs to implement DacDbiImpl.IsValidObject. It also adds a new CoreCLR cDAC global (ContinuationSingletonEEClass) to enable continuation subtype identification.

Changes:

• Adds a new CoreCLR cDAC global pointer (ContinuationSingletonEEClass) and wires it into the managed reader contracts/tests.
• Extends IRuntimeTypeSystem / RuntimeTypeSystem_1 with APIs to query EEClass pointers, canonical MethodTables, and continuation-without-metadata detection.
• Implements Microsoft.Diagnostics.DataContractReader.Legacy.DacDbiImpl.IsValidObject using the cDAC contracts and adds new MethodTable tests.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/native/managed/cdac/tests/MockDescriptors/MockDescriptors.RuntimeTypeSystem.cs	Adds mock global storage + setter for the continuation singleton EEClass pointer.
src/native/managed/cdac/tests/MethodTableTests.cs	Adds globals wiring and new theory tests for IsContinuationWithoutMetadata and IsCanonicalMethodTable.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/Dbi/DacDbiImpl.cs	Implements IsValidObject using cDAC contracts (replacing legacy fallback-only behavior).
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/RuntimeTypeSystem_1.cs	Reads new global and implements new RTS APIs (GetClassPointer, IsCanonicalMethodTable, IsContinuationWithoutMetadata).
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Constants.cs	Adds the new global name constant.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Abstractions/Contracts/IRuntimeTypeSystem.cs	Adds new public contract members used by IsValidObject.
src/coreclr/vm/datadescriptor/datadescriptor.inc	Exposes g_singletonContinuationEEClass via a new cDAC global pointer.

Comments suppressed due to low confidence (1)

src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/RuntimeTypeSystem_1.cs:548

• GetClassPointer is now a public IRuntimeTypeSystem API, but it doesn't guard against non-MethodTable TypeHandles (it indexes _methodTables[typeHandle.Address] unconditionally). Other public APIs in this type return TargetPointer.Null / 0 for non-MethodTable handles. Please add a typeHandle.IsMethodTable() check (and return TargetPointer.Null or throw ArgumentException consistently) to avoid KeyNotFound/undefined behavior when callers pass a TypeDesc handle.

    public TargetPointer GetClassPointer(TypeHandle typeHandle)
    {
        MethodTable methodTable = _methodTables[typeHandle.Address];
        switch (MethodTableFlags_1.GetEEClassOrCanonMTBits(methodTable.EEClassOrCanonMT))
        {

[rcj1]

No need to explicitly stack alloc, please follow the style of

runtime/src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/Dbi/DacDbiImpl.cs

Line 2819 in 30359c8

int hrLocal = _legacy.IsModuleMapped(pModule, &isModuleMappedLocal);

[rcj1]

Might want to have a dump test for this, see

runtime/src/native/managed/cdac/tests/DumpTests/DacDbi/DacDbiCCWDumpTests.cs

Line 31 in 30359c8

TargetPointer objectAddress = Target.ReadPointer(handleData.Handle);