fix markInputRules for italics mark

add another layer of matching by introducing support for second match group
since javascript (at least in current browsers) still lacks lookbehind in regex

so now supports

/nomatch(markstart(text)markend)nomatch/ and still supports the
/markstart(text)markend/ syntax

all `nomatch` will be kept as is so kindof simulating lookbehinds

packages/tiptap-extensions/src/marks/Italic.js

@@ -30,7 +30,8 @@ export default class Italic extends Mark {
 
   inputRules({ type }) {
     return [
-      markInputRule(/(?:^|[^*_])(?:\*|_)([^*_]+)(?:\*|_)$/, type),
+      markInputRule(/(?:^|[^_])(_([^_]+)_)$/, type),
+      markInputRule(/(?:^|[^*])(\*([^*]+)\*)$/, type),
     ]
   }