Compatibility cache lookup allocates Func for each lookup

[jebriede]

The CompatibilityProvider uses a cache in the check if frameworks are compatible. The code that checks the cache or adds an entry causes an allocation of a func on each lookup, causing an overallocation of objects.

Name                                                                      	Inc %	          Inc
 Type System.Func`2[NuGet.Frameworks.CompatibilityCacheKey,System.Boolean]	  0.6	   42,664,364
+ clr!?                                                                   	  0.6	   42,664,364
 + nuget.frameworks!CompatibilityProvider.IsCompatible                    	  0.6	   42,664,364