Join - shouldn't use new Dictionary<DValue<RecordValue>, bool>();

[MikeStall]

Join shouldn't use
DValue or RecordValue as a dictionary key.

Power-Fx/src/libraries/Microsoft.PowerFx.Interpreter/Functions/LibraryTable.cs

Line 584 in cce6c4b

var innerDict = new Dictionary<DValue<RecordValue>, bool>();

Fx does not have language semantics for RecordValue comparison.

Thing 1:
Join / Summarize / Distinct all have this same concept of comparing values. Can they share?

Function	How does it compare uniqueness?	Comments
Distinct:	Power-Fx/src/libraries/Microsoft.PowerFx.Interpreter/Functions/LibraryTable.cs Line 1318 in cce6c4b var key = distinctValue.ToObject();	Use ToObject, but only after a primitive check
Summarize	Power-Fx/src/libraries/Microsoft.PowerFx.Interpreter/Functions/LibraryTable.cs Line 1452 in cce6c4b var key = keyRecord.ToExpression();	Uses RecordValue.ToExpression. This is probably dangerous. is ToExpression always deterministic?
Join	Power-Fx/src/libraries/Microsoft.PowerFx.Interpreter/Functions/LibraryTable.cs Line 584 in cce6c4b var innerDict = new Dictionary<DValue<RecordValue>, bool>();	uses DValue as a key.

Can we standardize on Distinct's approach?

Thing 2:
Maybe even Dvalue.Equals should throw? RecordValue.Equals throw?
This is probably a larger breaking change - but would flush out bad usage.