cue/load: replace readimports with cueimports.Read

Pretty much the same code inherited from Go.
The way cue/load used it already matched the cueimports.Read API.

While here, fileProcessor.add only needs to use cue/parser to read
a CUE file's package clause and imported package paths,
so there is no need to parse comments at all.

Signed-off-by: Daniel Martí <mvdan@mvdan.cc>
Change-Id: I67c5349dd691b282a8c4c1fbd3dd5daaf7f10163
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1194965
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>
Reviewed-by: Roger Peppe <rogpeppe@gmail.com>

cue/load/loader_common.go

@@ -211,7 +211,7 @@ func (fp *fileProcessor) add(root string, file *build.File, mode importMode) (ad
 		return false
 	}
 
-	pf, perr := parser.ParseFile(fullPath, data, parser.ImportsOnly, parser.ParseComments)
+	pf, perr := parser.ParseFile(fullPath, data, parser.ImportsOnly)
 	if perr != nil {
 		badFile(errors.Promote(perr, "add failed"))
 		return true

cue/load/match.go

@@ -21,6 +21,7 @@ import (
 	"cuelang.org/go/cue/build"
 	"cuelang.org/go/cue/errors"
 	"cuelang.org/go/cue/token"
+	"cuelang.org/go/internal/cueimports"
 )
 
 // A match represents the result of matching a single package pattern.
@@ -74,7 +75,7 @@ func matchFile(cfg *Config, file *build.File, returnImports bool, allTags map[st
 		return false, nil, err
 	}
 
-	data, err = readImports(f, false, nil)
+	data, err = cueimports.Read(f)
 	f.Close()
 	if err != nil {
 		return false, nil,