Revise MSIDOauth2Factory

[antrix1989]

Decide if we need to move out logic that is not related to json parsing from this class. In particular, these methods:

@property (readonly) MSIDWebviewFactory *webviewFactory;
- (NSString *)cacheEnvironmentFromEnvironment:(NSString *)originalEnvironment context:(id<MSIDRequestContext>)context;
- (NSArray<NSString *> *)defaultCacheAliasesForEnvironment:(NSString *)originalEnvironment;