[wasm] Set the $RUNTIMESRCDIR$ for interpreter

[radekdoulik]

Fixes:

The "WasmAppBuilder" task failed unexpectedly.
System.ArgumentException: File MainJS='$RUNTIMESRCDIR$\src\mono\wasm\runtime-test.js' doesn't exist.
   at WasmAppBuilder.Execute() in WasmAppBuilder.dll:token 0x6000042+0x27
   at Microsoft.Build.BackEnd.TaskExecutionHost.Microsoft.Build.BackEnd.ITaskExecutionHost.Execute() in Microsoft.Build.dll:token 0x6001602+0x3e
   at Microsoft.Build.BackEnd.TaskBuilder.ExecuteInstantiatedTask(ITaskExecutionHost taskExecutionHost, TaskLoggingContext taskLoggingContext, TaskHost taskHost, ItemBucket bucket, TaskExecutionMode howToExecuteTask) in Microsoft.Build.dll:token 0x6001481+0x2b5

[naricc]

I think we also need to (or atleast should) change some of the commandline argument validation here:

BenchmarkDotNet/src/BenchmarkDotNet/ConsoleArguments/ConfigParser.cs

Line 115 in 1a94d4d

else if (runtimeMoniker == RuntimeMoniker.Wasm && !(options.AOTCompilerMode == MonoAotCompilerMode.wasm) && (options.WasmMainJs == null || options.WasmMainJs.IsNotNullButDoesNotExist()))

[adamsitnik]

Since the other part of the PR uses RuntimeSrcDir I would expect it to be validaten in this PR?

BenchmarkDotNet/src/BenchmarkDotNet/ConsoleArguments/ConfigParser.cs

Lines 124 to 128 in 5196e6f

	else if (runtimeMoniker == RuntimeMoniker.Wasm && options.AOTCompilerMode == MonoAotCompilerMode.wasm && (options.RuntimeSrcDir == null || options.RuntimeSrcDir.IsNotNullButDoesNotExist()))
	{
	logger.WriteLineError($"The provided {nameof(options.RuntimeSrcDir)} \"{options.RuntimeSrcDir}\" does NOT exist. It MUST be provided.");
	return false;
	}

[naricc]

@adamsitnik Radek is on vacation and I could not push to his branch, so I created another PR to keep iterating on this: #1763.

I think we can close this PR (1759).