Mono repo -> Master (#22553)

Combines the following repositories into one:

https://github.com/mattermost/mattermost-server
https://github.com/mattermost/mattermost-webapp
https://github.com/mattermost/focalboard
https://github.com/mattermost/mattermost-plugin-playbooks

server/tests/test-syntax-highlighting.md

@@ -0,0 +1,180 @@
+# Code Syntax Highlighting
+
+Verify the following code blocks render as code blocks and highlight properly. 
+
+### Diff
+
+``` diff
+*** /path/to/original	''timestamp''
+--- /path/to/new	''timestamp''
+***************
+*** 1 ****
+! This is a line.
+--- 1 ---
+! This is a replacement line.
+It is important to spell
+-removed line
++new line
+```
+
+### Makefile
+
+``` makefile
+CC=gcc
+CFLAGS=-I.
+
+hellomake: hellomake.o hellofunc.o
+     $(CC) -o hellomake hellomake.o hellofunc.o -I.
+```
+
+### JSON
+
+``` json
+{"employees":[
+    {"firstName":"John", "lastName":"Doe"},
+]}
+```
+
+### Markdown
+
+``` markdown
+**bold** 
+*italics* 
+[link](www.example.com)
+```
+
+### JavaScript
+
+``` javascript
+document.write('Hello, world!');
+```
+
+### CSS
+
+``` css
+body {
+    background-color: red;
+}
+```
+
+### Objective C
+
+``` objectivec
+#import <stdio.h>
+
+int main (void)
+{
+	printf ("Hello world!\n");
+}
+```
+
+### Python
+
+``` python
+print "Hello, world!"
+```
+
+### XML
+
+``` xml
+<employees>
+    <employee>
+        <firstName>John</firstName> <lastName>Doe</lastName>
+    </employee>
+</employees>
+```
+
+### Perl
+
+``` perl
+print "Hello, World!\n";
+```
+
+### Bash
+
+``` bash
+echo "Hello World"
+```
+
+### PHP
+
+``` php
+ <?php echo '<p>Hello World</p>'; ?> 
+```
+
+### CoffeeScript
+
+``` coffeescript
+console.log(“Hello world!”);
+```
+
+### C#
+
+``` cs
+using System;
+class Program
+{
+    public static void Main(string[] args)
+    {
+        Console.WriteLine("Hello, world!");
+    }
+}
+```
+
+### C++
+
+``` cpp
+#include <iostream.h>
+
+main()
+{
+    cout << "Hello World!";
+    return 0;
+}
+```
+
+### SQL 
+
+``` sql
+SELECT column_name,column_name
+FROM table_name;
+```
+
+### Go
+
+``` go
+package main
+import "fmt"
+func main() {
+    fmt.Println("Hello, 世界")
+}
+```
+
+### Ruby
+
+``` ruby
+puts "Hello, world!"
+```
+
+### Java
+
+``` java
+import javax.swing.JFrame;  //Importing class JFrame
+import javax.swing.JLabel;  //Importing class JLabel
+public class HelloWorld {
+    public static void main(String[] args) {
+        JFrame frame = new JFrame();           //Creating frame
+        frame.setTitle("Hi!");                 //Setting title frame
+        frame.add(new JLabel("Hello, world!"));//Adding text to frame
+        frame.pack();                          //Setting size to smallest
+        frame.setLocationRelativeTo(null);     //Centering frame
+        frame.setVisible(true);                //Showing frame
+    }
+}
+```
+
+### Latex Equation
+
+``` latex
+\frac{d}{dx}\left( \int_{0}^{x} f(u)\,du\right)=f(x).
+```