Update debugger packages, move to PortableInterop IMetadataImport (#80063)

As outlined in
microsoft/ConcordExtensibilitySamples#124, the
debugger will be breaking the public definition of `IMetadataImport`.
This change updates the debugger package versions to latest versions in
order to pick up the new definition under the
`Microsoft.MetadataReader.PortableInterop` namespace and migrates the
Roslyn usage off of the debugger definition in
`Microsoft.MetadataReader.IMetadataImport`. This also updates the
`DkmMetadataImportHolder` mock to expose the same property as the real
class, `

Notably the new definition no longer uses `StringBuilder` marshalling,
which should nominally improve performance.

Author: dibarbet

eng/Directory.Packages.props

@@ -122,8 +122,8 @@
       VS Debugger
     -->
     <PackageVersion Include="Microsoft.VisualStudio.Debugger.Contracts" Version="18.0.0-beta.25379.1" />
-    <PackageVersion Include="Microsoft.VisualStudio.Debugger.Engine-implementation" Version="17.13.1121201-preview" />
-    <PackageVersion Include="Microsoft.VisualStudio.Debugger.Metadata-implementation" Version="17.13.1121201-preview" />
+    <PackageVersion Include="Microsoft.VisualStudio.Debugger.Engine-implementation" Version="18.0.1082202-preview" />
+    <PackageVersion Include="Microsoft.VisualStudio.Debugger.Metadata-implementation" Version="18.0.1082202-preview" />
 
     <!--
       VS .NET Runtime

src/ExpressionEvaluator/Core/Source/ResultProvider/Formatter.cs

@@ -17,6 +17,7 @@
 using Microsoft.VisualStudio.Debugger.Evaluation;
 using Microsoft.VisualStudio.Debugger.Evaluation.ClrCompilation;
 using Type = Microsoft.VisualStudio.Debugger.Metadata.Type;
+using Token = System.Reflection.Adds.Token;
 
 namespace Microsoft.CodeAnalysis.ExpressionEvaluator
 {
@@ -182,23 +183,24 @@ string IDkmClrFullNameProvider2.GetClrNameForLocalVariable(DkmInspectionContext
         string IDkmClrFullNameProvider2.GetClrNameForField(DkmInspectionContext inspectionContext, DkmClrModuleInstance moduleInstance, int fieldToken)
         {
             using var importHolder = moduleInstance.GetMetaDataImportHolder();
+            Token tkField = new Token(fieldToken);
 
             // Just get some of information about properties. Get rest later only if needed.
-            int hr = importHolder.Value.GetFieldProps(fieldToken, out _, null, 0, out var nameLength, out _, out _, out _, out _, out _, out _);
+            int hr = importHolder.PortableValue.GetFieldProps(tkField, out _, null, 0, out uint nameLength, out _, out _, out _, out _, out _, out _);
             const int S_OK = 0;
             if (hr != S_OK)
             {
                 throw new ArgumentException("Invalid field token.", nameof(fieldToken));
             }
 
-            var sb = new StringBuilder(nameLength);
-            hr = importHolder.Value.GetFieldProps(fieldToken, out _, sb, sb.Capacity, out _, out _, out _, out _, out _, out _, out _);
+            char[] szField = new char[nameLength];
+            hr = importHolder.PortableValue.GetFieldProps(tkField, out _, szField, nameLength, out uint actualLength, out _, out _, out _, out _, out _, out _);
             if (hr != S_OK)
             {
                 throw new DkmException((DkmExceptionCode)hr);
             }
 
-            string metadataName = sb.ToString();
+            string metadataName = actualLength > 0 ? new string(szField, 0, (int)actualLength - 1) : string.Empty;
             return GetOriginalFieldName(metadataName);
         }