Some lookup diagnostics may be missed when a file type shadows a non-file type

[RikkiGibson]

Related to #61500, #60819

roslyn/src/Compilers/CSharp/Portable/Binder/Binder_Symbols.cs

Lines 1819 to 1826 in a540733

	if (best.IsFromFile && !secondBest.IsFromFile)
	{
	// a lookup of a file type is "better" than a lookup of a non-file type; no need to further diagnose
	// PROTOTYPE(ft): some "single symbol" diagnostics are missed here for similar reasons
	// that make us miss diagnostics when reporting WRN_SameFullNameThisAggAgg.
	//
	return first;
	}