cmd/cue: map constants by go/types.Type directly
The type values make good map keys already, as they are unique for each
Go type and they can be compared. There's no need to stringify.
While here, remove an unnecessary String method call with %s.
Signed-off-by: Daniel Martí <mvdan@mvdan.cc>
Change-Id: Ie03fae7220158ddb45582d25e7e7c431a70328ce
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1230087
Reviewed-by: Matthew Sackman <matthew@cue.works>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>