[Isabel Duan (iisaduan)]

fixes #50603, which bisected to #49119

Previously: unconstrained type parameters were inconsistently checked in comparisons, as shown below (5.5.3 playground):

function f<T>(a: T, b: T) {
   return a > b; \\ okay
}

function g<T extends {} | undefined | null>(a: T, b: T) {
   return a > b; \\ error!! 
      \\ 'a' is possibly 'null' or 'undefined'.ts(18049)
      \\ 'b' is possibly 'null' or 'undefined'.ts(18049)
}

Now with this PR:

    function f1<T>(a: T, b: T): boolean {
        return a > b;
               ~
!!! error TS18046: 'a' is of type 'unknown'.
                   ~
!!! error TS18046: 'b' is of type 'unknown'.
    }
    
    function f2<T extends {} | undefined | null>(a: T, b: T): boolean {
        return a > b;
               ~
!!! error TS18049: 'a' is possibly 'null' or 'undefined'.
                   ~
!!! error TS18049: 'b' is possibly 'null' or 'undefined'.
    }    

This PR does not affect the checking of unconstrained types in other locations.