Escape markdown sequences (#2208)

* escape inline markdown character

* fix typo

* improve document around custom markdown plugin and add escape sequence utils

* recover inline escape sequences on edit

* remove escape sequences from plain text body

* use `s` for strike-through instead of del

* escape block markdown sequences

* fix remove escape sequence was not removing all slashes from plain text

* recover block sequences on edit

src/app/plugins/markdown/block/runner.ts

@@ -0,0 +1,25 @@
+import { replaceMatch } from '../internal';
+import { BlockMDParser, BlockMDRule } from './type';
+
+/**
+ * Parses block-level markdown text into HTML using defined block rules.
+ *
+ * @param text - The text to parse.
+ * @param rule - The markdown rule to run.
+ * @param parse - A function that run the parser on remaining parts..
+ * @param parseInline - Optional function to parse inline elements.
+ * @returns The text with the markdown rule applied or `undefined` if no match is found.
+ */
+export const runBlockRule = (
+  text: string,
+  rule: BlockMDRule,
+  parse: BlockMDParser,
+  parseInline?: (txt: string) => string
+): string | undefined => {
+  const matchResult = rule.match(text);
+  if (matchResult) {
+    const content = rule.html(matchResult, parseInline);
+    return replaceMatch(text, matchResult, content, (txt) => [parse(txt, parseInline)]).join('');
+  }
+  return undefined;
+};