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/indented_code.go

@@ -0,0 +1,98 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package markdown
+
+import (
+	"strings"
+)
+
+type IndentedCodeLine struct {
+	Indentation int
+	Range       Range
+}
+
+type IndentedCode struct {
+	blockBase
+	markdown string
+
+	RawCode []IndentedCodeLine
+}
+
+func (b *IndentedCode) Code() (result string) {
+	for _, code := range b.RawCode {
+		result += strings.Repeat(" ", code.Indentation) + b.markdown[code.Range.Position:code.Range.End]
+	}
+	return
+}
+
+func (b *IndentedCode) Continuation(indentation int, r Range) *continuation {
+	if indentation >= 4 {
+		return &continuation{
+			Indentation: indentation - 4,
+			Remaining:   r,
+		}
+	}
+	s := b.markdown[r.Position:r.End]
+	if strings.TrimSpace(s) == "" {
+		return &continuation{
+			Remaining: r,
+		}
+	}
+	return nil
+}
+
+func (b *IndentedCode) AddLine(indentation int, r Range) bool {
+	b.RawCode = append(b.RawCode, IndentedCodeLine{
+		Indentation: indentation,
+		Range:       r,
+	})
+	return true
+}
+
+func (b *IndentedCode) Close() {
+	for {
+		last := b.RawCode[len(b.RawCode)-1]
+		s := b.markdown[last.Range.Position:last.Range.End]
+		if strings.TrimRight(s, "\r\n") == "" {
+			b.RawCode = b.RawCode[:len(b.RawCode)-1]
+		} else {
+			break
+		}
+	}
+}
+
+func (b *IndentedCode) AllowsBlockStarts() bool {
+	return false
+}
+
+func indentedCodeStart(markdown string, indentation int, r Range, matchedBlocks, unmatchedBlocks []Block) []Block {
+	if len(unmatchedBlocks) > 0 {
+		if _, ok := unmatchedBlocks[len(unmatchedBlocks)-1].(*Paragraph); ok {
+			return nil
+		}
+	} else if len(matchedBlocks) > 0 {
+		if _, ok := matchedBlocks[len(matchedBlocks)-1].(*Paragraph); ok {
+			return nil
+		}
+	}
+
+	if indentation < 4 {
+		return nil
+	}
+
+	s := markdown[r.Position:r.End]
+	if strings.TrimSpace(s) == "" {
+		return nil
+	}
+
+	return []Block{
+		&IndentedCode{
+			markdown: markdown,
+			RawCode: []IndentedCodeLine{{
+				Indentation: indentation - 4,
+				Range:       r,
+			}},
+		},
+	}
+}