Set code languages for various files (part 1) (#28145)

* Set code languages for various files (part 1)

* Revert LaTeX change for now

* Update files/en-us/web/api/performance_api/server_timing/index.md

Co-authored-by: Brian Thomas Smith <[email protected]>

* Update files/en-us/learn/javascript/building_blocks/conditionals/index.md

Co-authored-by: Joshua Chen <[email protected]>

* Update files/en-us/learn/javascript/first_steps/variables/index.md

Co-authored-by: Joshua Chen <[email protected]>

* Fix selected languages

* Fix selected languages

* Fix selected languages

* Apply suggestions from code review

Co-authored-by: Joshua Chen <[email protected]>

---------

Co-authored-by: Brian Thomas Smith <[email protected]>
Co-authored-by: Joshua Chen <[email protected]>

Author: 3 people

LICENSE.md

@@ -11,7 +11,7 @@ All prose content is available under
 
 ### Text of CC-BY-SA-2.5 license
 
-```
+```plain
 Creative Commons Attribution-ShareAlike 2.5
 
 CREATIVE COMMONS CORPORATION IS NOT A LAW FIRM AND DOES NOT PROVIDE LEGAL SERVICES. DISTRIBUTION OF THIS LICENSE DOES NOT CREATE AN ATTORNEY-CLIENT RELATIONSHIP. CREATIVE COMMONS PROVIDES THIS INFORMATION ON AN "AS-IS" BASIS. CREATIVE COMMONS MAKES NO WARRANTIES REGARDING THE INFORMATION PROVIDED, AND DISCLAIMS LIABILITY FOR DAMAGES RESULTING FROM ITS USE.
@@ -75,13 +75,13 @@ Code examples and snippets added on or after August 20, 2010 are in the public d
 ([CC0](https://creativecommons.org/publicdomain/zero/1.0/legalcode)). No licensing notice
 is necessary, but if you need one, you can use:
 
-```
+```plain
 Any copyright is dedicated to the Public Domain. http://creativecommons.org/publicdomain/zero/1.0/
 ```
 
 #### Text of CC0 license
 
-```
+```plain
 Creative Commons Legal Code
 
 CC0 1.0 Universal
@@ -211,13 +211,13 @@ Code examples and snippets added before August 20, 2010 are available under
 the [MIT license](https://opensource.org/licenses/MIT). You should insert
 the following attribution information into the MIT license template:
 
-```
+```plain
 © <date of last page revision> <name of person who created it>
 ```
 
 #### Text of MIT license template
 
-```
+```plain
 Copyright <YEAR> <COPYRIGHT HOLDER>
 
 Permission is hereby granted, free of charge, to any person obtaining a copy of this

files/en-us/glossary/base64/index.md

@@ -10,7 +10,7 @@ page-type: glossary-definition
 
 When the term "Base64" is used on its own to refer to a specific algorithm, it typically refers to the version of Base64 outlined in [RFC 4648](https://datatracker.ietf.org/doc/html/rfc4648), section 4, which uses the following alphabet to represent the radix-64 digits, alongside `=` as a padding character:
 
-```
+```plain
 ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/
 ```