Add GetField and GetField holes
Move new field creation to Sugar
GetField as operator
Sugar.GetField lenses
Sugar.holeResultPick returns whether result has holes
refactored Sugar.uninferredHoles
Oops: Hole guid targets were wrong
inferredHoles: Support GetField field tag holes
Revert "inferredHoles: Support GetField field tag holes"

This reverts commit d85262aca08af68b72bd32b076a4165962fddbac.
Refactor: matchBody is more type-safe
Rules: Avoid unsafe lists
Oops: Tests were broken
Towards Tags as expressions
Towards Tags as expressions: simple type rule
Only one ChildrenToParent structure rule
Only one ParentToChildren structure rule
Towards Tags as expressions: GetField as operator on both sides
{Expression,Sugar}.GetField have record first, tag second
Reuse ParentToChildren for record field types to record type's field types
No need to copy initial stored expressions to the inferred vals, ChildrenToParent handles it