Editorial: Cleanup ValidateAndApplyPropertyDescriptor and own prop operations (#2468)

 - Merge tables in sec-property-attributes
 - Clarify Proxy [[GetOwnProperty]]
 - Improve ValidateAndApplyPropertyDescriptor structured header
 - Simplify the ValidateAndApplyPropertyDescriptor new-property case
 - Refactor ValidateAndApplyPropertyDescriptor for comprehensibility
 - Further refactor ValidateAndApplyPropertyDescriptor
 - Add "fully populated Property Descriptor" definition and assertion
 - Merge checks that effect [[Value]]/[[Data]] immutability
 - Rename alias
 - Remove field name indirection

Fixes #2466

Author: gibson042