Moving markdown to corelibs (#16916)

* Moving markdown to corelibs

* Fix golangci-lint problem

* Renaming corelibs to pkg

* Fixing golangci-lint

* Renaming from pkg to shared

* Fixing gofmt

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

shared/markdown/lines_test.go

@@ -0,0 +1,36 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package markdown
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestParseLines(t *testing.T) {
+	assert.Equal(t, []Line{
+		{Range{0, 4}}, {Range{4, 7}},
+	}, ParseLines("foo\nbar"))
+
+	assert.Equal(t, []Line{
+		{Range{0, 5}}, {Range{5, 8}},
+	}, ParseLines("foo\r\nbar"))
+
+	assert.Equal(t, []Line{
+		{Range{0, 4}}, {Range{4, 6}}, {Range{6, 9}},
+	}, ParseLines("foo\r\r\nbar"))
+
+	assert.Equal(t, []Line{
+		{Range{0, 4}},
+	}, ParseLines("foo\n"))
+
+	assert.Equal(t, []Line{
+		{Range{0, 4}},
+	}, ParseLines("foo\r"))
+
+	assert.Equal(t, []Line{
+		{Range{0, 5}},
+	}, ParseLines("foo\r\n"))
+}