Desktop: Improved GotoAnything speed and made it safer

Previously we'd use the remove-markdown package to create the note
preview however this function would freeze on certain notes, and was
probably unsafe as it used regex to parse Markdown. Replaced this in
favour of Markdown-it along with htmlparser2 to strip all markup from a
note.

ReactNativeClient/lib/htmlUtils.js

@@ -1,6 +1,7 @@
 const urlUtils = require('lib/urlUtils.js');
 const Entities = require('html-entities').AllHtmlEntities;
 const htmlentities = new Entities().encode;
+const htmlparser2 = require('htmlparser2');
 
 // [\s\S] instead of . for multiline matching
 // https://stackoverflow.com/a/16119722/561309
@@ -107,6 +108,41 @@ class HtmlUtils {
 
 		return output.join(' ');
 	}
+
+	stripHtml(html) {
+		const output = [];
+
+		const tagStack = [];
+
+		const currentTag = () => {
+			if (!tagStack.length) return '';
+			return tagStack[tagStack.length - 1];
+		};
+
+		const disallowedTags = ['script', 'style', 'head', 'iframe', 'frameset', 'frame', 'object', 'base'];
+
+		const parser = new htmlparser2.Parser({
+
+			onopentag: (name) => {
+				tagStack.push(name.toLowerCase());
+			},
+
+			ontext: (decodedText) => {
+				if (disallowedTags.includes(currentTag())) return;
+				output.push(decodedText);
+			},
+
+			onclosetag: (name) => {
+				if (currentTag() === name.toLowerCase()) tagStack.pop();
+			},
+
+		}, { decodeEntities: true });
+
+		parser.write(html);
+		parser.end();
+
+		return output.join('').replace(/\s+/g, ' ');
+	}
 }
 
 const htmlUtils = new HtmlUtils();