Document native regex syntax (#1019)

* document native regex syntax

* update more docs

Author: zth

misc_docs/syntax/extension_regular_expression.mdx

@@ -6,6 +6,8 @@ summary: "This is the `regular expression` extension point."
 category: "extensionpoints"
 ---
 
+> Deprecated in favor of native regular expression syntax in v12+
+
 `%re` is used to create JavaScript regular expressions.
 
 <CodeTab labels={["ReScript", "JS Output"]}>

misc_docs/syntax/language_regular_expression.mdx

@@ -0,0 +1,31 @@
+---
+id: "regular-expression-syntax"
+keywords: ["regular", "expression", "regex"]
+name: "/re/"
+summary: "This is the `regular expression` syntax."
+category: "languageconstructs"
+---
+
+> Available in v12+
+
+You write regular expressions in ReScript just like you do in JavaScript.
+
+<CodeTab labels={["ReScript", "JS Output"]}>
+
+```res
+let regex = /^hello/
+let result = regex->RegExp.test("hello world")
+```
+
+```js
+let regex = /^hello/;
+
+let result = regex.test("hello world");
+```
+
+</CodeTab>
+
+### References
+
+* [Regular Expressions](/docs/manual/latest/primitive-types#regular-expression)
+* [RegExp API](/docs/manual/latest/api/core/regexp)

pages/docs/manual/v12.0.0/primitive-types.mdx

@@ -112,15 +112,15 @@ ReScript regular expressions compile cleanly to their JavaScript counterpart:
 <CodeTab labels={["ReScript", "JS Output"]}>
 
 ```res example
-let r = %re("/b/g")
+let r = /b/g
 ```
 ```js
-var r = /b/g;
+let r = /b/g;
 ```
 
 </CodeTab>
 
-A regular expression like the above has the type `Re.t`. The [RegExp](api/core/regexp) module contains the regular expression helpers you have seen in JS.
+A regular expression like the above has the type `RegExp.t`. The [RegExp](api/core/regexp) module contains the regular expression helpers you have seen in JS.
 
 ## Boolean