Fixes #335 (Unable to detect multiple parameter annotations with different RetentionPolicies). If a method parameter had annotations with both runtime-visible and runtime-invisible retention policies, only one of the two policy types would be stored in the MethodParameterInfo
for each method parameter. This fix merges together annotations from both retention policies, so that method parameter annotations from one of the two retention policies are not dropped. Thanks to @T101N for reporting, and for submitting extensive test case code.