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/inspect_test.go

@@ -0,0 +1,75 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package markdown
+
+import (
+	"fmt"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestInspect(t *testing.T) {
+	markdown := `
+[foo]: bar
+- a
+  > [![]()]()
+  > [![foo]][foo]
+- d
+`
+
+	visited := []string{}
+	level := 0
+	Inspect(markdown, func(blockOrInline interface{}) bool {
+		if blockOrInline == nil {
+			level--
+		} else {
+			visited = append(visited, strings.Repeat(" ", level*4)+strings.TrimPrefix(fmt.Sprintf("%T", blockOrInline), "*markdown."))
+			level++
+		}
+		return true
+	})
+
+	assert.Equal(t, []string{
+		"Document",
+		"    Paragraph",
+		"    List",
+		"        ListItem",
+		"            Paragraph",
+		"                Text",
+		"            BlockQuote",
+		"                Paragraph",
+		"                    InlineLink",
+		"                        InlineImage",
+		"                    SoftLineBreak",
+		"                    ReferenceLink",
+		"                        ReferenceImage",
+		"                            Text",
+		"        ListItem",
+		"            Paragraph",
+		"                Text",
+	}, visited)
+}
+
+var counterSink int
+
+func BenchmarkInspect(b *testing.B) {
+	text := `Some standard piece of text.
+
+Has a link [post](https://github.com) and also has a blockquote.
+
+> This is a famous quote.
+
+Some bold text **Text for markdown?** to go with it.
+
+At the end, some more lines`
+
+	for i := 0; i < b.N; i++ {
+		Inspect(text, func(_ interface{}) bool {
+			counterSink++
+			return true
+		})
+	}
+}