Perf: Avoid unnecessary ProjectMetadataInstance allocations

[ccastanedaucf]

Context

Fixes an allocation regression in a VS C++ scenario due to allocating ProjectMetadataInstance when retrieving metadata values in BatchingEngine.

Here's the trace pulled from VcxprojReader when loading the UE52 test solution in VS:

Changes Made

This refactors various methods so that ProjectItemInstance.GetMetadataEscaped can directly retrieve the escaped string value without intermediate ProjectMetadataInstance allocations.

[Copilot]

Pull Request Overview

This PR optimizes performance by eliminating unnecessary ProjectMetadataInstance allocations when retrieving metadata values in MSBuild's BatchingEngine. The changes refactor metadata retrieval methods to directly return escaped string values instead of creating intermediate ProjectMetadataInstance objects.

• Refactored GetMetadataEscaped to use string-based methods instead of metadata instance objects
• Updated GetItemDefinitionMetadata to return strings directly as GetItemDefinitionMetadataEscaped
• Optimized IMetadataTable.GetEscapedValueIfPresent to avoid unnecessary metadata object creation

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/Build/Instance/ProjectItemInstance.cs	Refactored metadata retrieval methods to work with escaped strings directly instead of allocating ProjectMetadataInstance objects
src/Build/Instance/ProjectItemDefinitionInstance.cs	Optimized GetEscapedValueIfPresent to return string values directly from metadata dictionary

[ccastanedaucf]

FYI the test failure is unrelated

�[37m    Microsoft.Build.Engine.UnitTests.BackEnd.TaskHostFactory_Tests.TaskNodesDieAfterBuild(taskHostFactorySpecified: False, envVariableSpecified: True) [PASS]
�[m�[30;1m      Output:
�[m�[37m        [02:55:29.980] Attached to Sidecar (PID 8174)
�[mUnhandled exception. System.InvalidOperationException: Process was not started by this object, so requested information cannot be determined.
   at System.Diagnostics.Process.EnsureState(State state)
   at System.Diagnostics.Process.get_ExitCode()
   at Microsoft.Build.Engine.UnitTests.BackEnd.TaskHostFactory_Tests.ProcessTracker.<>c__DisplayClass1_1.<AttachToProcess>b__0(Object sender, EventArgs e) in /home/vsts/work/1/s/src/Build.UnitTests/BackEnd/TaskHostFactory_Tests.cs:line 366
   at System.Diagnostics.Process.RaiseOnExited()
   at System.Diagnostics.Process.CompletionCallback(Object waitHandleContext, Boolean wasSignaled)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
--- End of stack trace from previous location ---
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.CompleteWaitThreadPoolWorkItem.System.Threading.IThreadPoolWorkItem.Execute()
   at System.Threading.ThreadPoolWorkQueue.Dispatch()
   at System.Threading.PortableThreadPool.WorkerThread.WorkerThreadStart()
   at System.Threading.Thread.StartCallback()