Fix ambiguous reference for ExceptionHandling class

[mthalman]

The latest daily build of the .NET 10 SDK fails to build the msbuild repo due to the following build error:

/repos/dotnet/src/msbuild/src/Build/BackEnd/BuildManager/BuildManager.cs(1330,41): error CS0104: 'ExceptionHandling' is an ambiguous reference between 'Microsoft.Build.Shared.ExceptionHandling' and 'System.Runtime.ExceptionServices.ExceptionHandling' [/repos/dotnet/src/msbuild/src/Build/Microsoft.Build.csproj]
/repos/dotnet/src/msbuild/src/Build/BackEnd/Components/ProjectCache/ProjectCacheService.cs(875,17): error CS0104: 'ExceptionHandling' is an ambiguous reference between 'Microsoft.Build.Shared.ExceptionHandling' and 'System.Runtime.ExceptionServices.ExceptionHandling' [/repos/dotnet/src/msbuild/src/Build/Microsoft.Build.csproj]
/repos/dotnet/src/msbuild/src/Build/BackEnd/BuildManager/BuildManager.cs(1437,57): error CS0104: 'ExceptionHandling' is an ambiguous reference between 'Microsoft.Build.Shared.ExceptionHandling' and 'System.Runtime.ExceptionServices.ExceptionHandling' [/repos/dotnet/src/msbuild/src/Build/Microsoft.Build.csproj]
/repos/dotnet/src/msbuild/src/Build/BackEnd/BuildManager/BuildManager.cs(1448,41): error CS0104: 'ExceptionHandling' is an ambiguous reference between 'Microsoft.Build.Shared.ExceptionHandling' and 'System.Runtime.ExceptionServices.ExceptionHandling' [/repos/dotnet/src/msbuild/src/Build/Microsoft.Build.csproj]
/repos/dotnet/src/msbuild/src/Build/BackEnd/BuildManager/BuildManager.cs(1584,17): error CS0104: 'ExceptionHandling' is an ambiguous reference between 'Microsoft.Build.Shared.ExceptionHandling' and 'System.Runtime.ExceptionServices.ExceptionHandling' [/repos/dotnet/src/msbuild/src/Build/Microsoft.Build.csproj]
/repos/dotnet/src/msbuild/src/Build/BackEnd/BuildManager/BuildManager.cs(1806,49): error CS0104: 'ExceptionHandling' is an ambiguous reference between 'Microsoft.Build.Shared.ExceptionHandling' and 'System.Runtime.ExceptionServices.ExceptionHandling' [/repos/dotnet/src/msbuild/src/Build/Microsoft.Build.csproj]
/repos/dotnet/src/msbuild/src/Build/BackEnd/BuildManager/BuildManager.cs(1879,21): error CS0104: 'ExceptionHandling' is an ambiguous reference between 'Microsoft.Build.Shared.ExceptionHandling' and 'System.Runtime.ExceptionServices.ExceptionHandling' [/repos/dotnet/src/msbuild/src/Build/Microsoft.Build.csproj]
/repos/dotnet/src/msbuild/src/Build/BackEnd/BuildManager/BuildManager.cs(1879,66): error CS0104: 'ExceptionHandling' is an ambiguous reference between 'Microsoft.Build.Shared.ExceptionHandling' and 'System.Runtime.ExceptionServices.ExceptionHandling' [/repos/dotnet/src/msbuild/src/Build/Microsoft.Build.csproj]
/repos/dotnet/src/msbuild/src/Build/BackEnd/BuildManager/BuildManager.cs(2483,44): error CS0104: 'ExceptionHandling' is an ambiguous reference between 'Microsoft.Build.Shared.ExceptionHandling' and 'System.Runtime.ExceptionServices.ExceptionHandling' [/repos/dotnet/src/msbuild/src/Build/Microsoft.Build.csproj]
/repos/dotnet/src/msbuild/src/Build/BackEnd/BuildManager/BuildManager.cs(2484,161): error CS0104: 'ExceptionHandling' is an ambiguous reference between 'Microsoft.Build.Shared.ExceptionHandling' and 'System.Runtime.ExceptionServices.ExceptionHandling' [/repos/dotnet/src/msbuild/src/Build/Microsoft.Build.csproj]
/repos/dotnet/src/msbuild/src/Build/BackEnd/BuildManager/BuildManager.cs(2493,169): error CS0104: 'ExceptionHandling' is an ambiguous reference between 'Microsoft.Build.Shared.ExceptionHandling' and 'System.Runtime.ExceptionServices.ExceptionHandling' [/repos/dotnet/src/msbuild/src/Build/Microsoft.Build.csproj]
/repos/dotnet/src/msbuild/src/Build/BackEnd/BuildManager/BuildManager.cs(2976,41): error CS0104: 'ExceptionHandling' is an ambiguous reference between 'Microsoft.Build.Shared.ExceptionHandling' and 'System.Runtime.ExceptionServices.ExceptionHandling' [/repos/dotnet/src/msbuild/src/Build/Microsoft.Build.csproj]

This is due to a conflict in a class name with a new public class from runtime: dotnet/runtime#109806

Fixed by explicitly defining the namespace to use.

This was found as part of the work on dotnet/sdk#45435.