test/Utils: hole -> pureHole
test/ make alias for pure expressions
test/ make alias for pure expressions with DefI get-defs
test/ InferResults hard-coded for DefI t
test/ Remove mk/make[inferred] prefixes on functions. Use concise names
ExprUtil: Add lam/lambda/pi prisms
Move Infer.Rules.subst to ExprUtil
inferExpr takes only the InferResults. No need to build pure expr, it is the voided InferResults
Refactor ExprUtil.lens and move them into ExprLens