PHP: Added readonly keyword (#3349)

Co-authored-by: RunDevelopment <mitchi5000.ms@googlemail.com>

components/prism-php.js

@@ -100,7 +100,7 @@
 				//
 				// keywords cannot be preceded by "->"
 				// the complex lookbehind means `(?<!(?:->|::)\s*)`
-				pattern: /((?:^|[^\s>:]|(?:^|[^-])>|(?:^|[^:]):)\s*)\b(?:abstract|and|array|as|break|callable|case|catch|clone|const|continue|declare|default|die|do|echo|else|elseif|empty|enddeclare|endfor|endforeach|endif|endswitch|endwhile|enum|eval|exit|extends|final|finally|fn|for|foreach|function|global|goto|if|implements|include|include_once|instanceof|insteadof|interface|isset|list|match|namespace|new|or|parent|print|private|protected|public|require|require_once|return|self|static|switch|throw|trait|try|unset|use|var|while|xor|yield|__halt_compiler)\b/i,
+				pattern: /((?:^|[^\s>:]|(?:^|[^-])>|(?:^|[^:]):)\s*)\b(?:abstract|and|array|as|break|callable|case|catch|clone|const|continue|declare|default|die|do|echo|else|elseif|empty|enddeclare|endfor|endforeach|endif|endswitch|endwhile|enum|eval|exit|extends|final|finally|fn|for|foreach|function|global|goto|if|implements|include|include_once|instanceof|insteadof|interface|isset|list|match|namespace|new|or|parent|print|private|protected|public|readonly|require|require_once|return|self|static|switch|throw|trait|try|unset|use|var|while|xor|yield|__halt_compiler)\b/i,
 				lookbehind: true
 			}
 		],

tests/languages/php/keyword_feature.test

@@ -55,6 +55,7 @@ print
 private
 protected
 public
+readonly
 require
 require_once
 return
@@ -135,6 +136,7 @@ yield from
 	["keyword", "private"],
 	["keyword", "protected"],
 	["keyword", "public"],
+	["keyword", "readonly"],
 	["keyword", "require"],
 	["keyword", "require_once"],
 	["keyword", "return"],