chore: Update LangVersion to 14

[filzrev]

This PR update LangVersion from 12 to 14.

After this PR is merged.
BenchmarkDotNet source build requires .NET 10 SDK.

Other changes

1. build/sdk/global.json

Update SDK version to 10.0.100 to use LangVersion 14.
This setting seems also applied to unit tests. (By existing roll forward setting)
So by this change. tests app that build target net80 are executed under .NET 10 runtime.

2. src/BenchmarkDotNet/Code/DeclarationsProvider.cs

Rename field variable name to fieldInfo to fix build error that occurred when using field property name on C# 14.

3. build\BenchmarkDotNet.Build\Program.cs

Add steps to install wasm-tools-net8 workload.
When build .NET 8 WASM project with .NET SDK 10.
It need to install additional workload.
https://learn.microsoft.com/en-us/aspnet/core/blazor/webassembly-build-tools-and-aot?view=aspnetcore-10.0#net-webassembly-build-tools

4. tests/BenchmarkDotNet.IntegrationTests/NugetReferenceTests.cs

When build project with .NET 10 SDK.
System.Collection.Immutable package is pruned and resolved to SDK version assembly.
So I've added code for custom comparison.

5.
tests/BenchmarkDotNet.IntegrationTests/MultipleRuntimesTest.cs
tests/BenchmarkDotNet.IntegrationTests/LargeAddressAwareTest.cs
tests/BenchmarkDotNet.Tests/RuntimeVersionDetectionTests.cs
tests/BenchmarkDotNet.Tests/Helpers/DotNetRuntimeHelper.cs

Modify assertion logics to support environment that using DOTNET_ROLL_FORWARD_ON_NO_CANDIDATE_FX=2.

[filzrev]

Following tests failed on CI environment (It's passed on local environment)

Failed CurrentRuntimeIsProperlyRecognized [1 ms]
Error Message:
 Actual runtime: .NET 10.0, tfm: net10.0, moniker: Net10_0
Stack Trace:
  at BenchmarkDotNet.Tests.RuntimeVersionDetectionTests.CurrentRuntimeIsProperlyRecognized() in /home/runner/work/BenchmarkDotNet/BenchmarkDotNet/tests/BenchmarkDotNet.Tests/RuntimeVersionDetectionTests.cs:line 123
  at System.Reflection.MethodBaseInvoker.InterpretedInvoke_Method(Object obj, IntPtr* args)
  at System.Reflection.MethodBaseInvoker.InvokeWithNoArgs(Object obj, BindingFlags invokeAttr)

Not only for build stage.
.NET 8 targeted tests are also executed on .NET 10 runtime

It seems DOTNET_ROLL_FORWARD_ON_NO_CANDIDATE_FX=2 settings affecting this behavior differences.