encoding/csv: preserve \r\n in quoted fields

The parser mistakenly assumed it could always fold \r\n into \n, which
is not true since a \r\n inside a quoted fields has no special meaning
and should be kept as is.

Fix this by not folding \r\n to \n inside quotes fields.

Fixes #21201

Change-Id: Ifebc302e49cf63e0a027ee90f088dbc050a2b7a6
Reviewed-on: https://go-review.googlesource.com/52810
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/encoding/csv/reader_test.go

@@ -284,6 +284,13 @@ x,,,
 		Line:   2,
 		Column: 2,
 	},
+	{ // issue 21201
+		Name:  "CRLFInQuotedField",
+		Input: "\"Hello\r\nHi\"",
+		Output: [][]string{
+			{"Hello\r\nHi"},
+		},
+	},
 }
 
 func TestRead(t *testing.T) {