internal/diff: use compact printing mode
internal/diff: use compact printing mode

The default Syntax printing mode is not suitable.
We should print evaluated values.

Change-Id: I810b531f5898fcca049ac8943c5492e558f89ee5
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/6660
Reviewed-by: CUE cueckoo <0f32a827c9a5f00281f936ac78b5ef3ba80a954c@gmail.com>
Reviewed-by: Marcel van Lohuizen <a22d082192f3ccf984644a4f482781f4c2d65180@golang.org>

cuelang/cue