stylelint: Enable selector-pseudo-element-colon-notation

Via stylelint --fix

Change-Id: Iafee0799add6495119f174d3022af17206167c0e

.stylelintrc.json

@@ -4,7 +4,6 @@
 		"stylelint-config-wikimedia/mediawiki"
 	],
 	"rules": {
-		"selector-class-pattern": "(tdg|mw|oo-ui|cdx|client|skin)-",
-		"selector-pseudo-element-colon-notation": null
+		"selector-class-pattern": "(tdg|mw|oo-ui|cdx|client|skin)-"
 	}
 }

modules/ext.templateDataGenerator.editTemplatePage/templateDataGenerator.placeholder.less

@@ -1,4 +1,4 @@
-.client-js .tdg-editscreen-placeholder:after {
+.client-js .tdg-editscreen-placeholder::after {
 	content: '\00a0';
 	display: block;
 	line-height: 1.42857143em; /* Mirroring the button's line-height */