Fix excess property check in union and intersection types

[Anders Hejlsberg (ahejlsberg)]

Fixes #5237.

[Daniel Rosenwasser (DanielRosenwasser)]

Nice test

[Ryan Cavanaugh (RyanCavanaugh)]

You should have phrased that using four words

[Daniel Rosenwasser (DanielRosenwasser)]

LGTM

[Mohamed Hegazy (mhegazy)]

👍

[Anders Hejlsberg (ahejlsberg)]

The PR modifies the rules for excess properties as follows:

A source type S is considered to have excess properties with respect to a target type T if

• S is a fresh object literal type,
• T is an object-like type, and
• S has one or more properties that aren't expected in T.

A type T is said to be object-like if

• T is an object type, or
• T a union or intersection type containing at least one-object like type.

A property P is said to be expected in a type T if one of the following is true:

• T is an object type and
  • T has a property with the same name as P,
  • T has a string or numeric index signature,
  • T has no properties, or
  • T is the global type 'Object'.
• T is a union or intersection type and P is expected in at least one object-like constituent type of T.