Add unicode support for TH quotes (`[| |]`)

This has been mentioned before but didn't have it's own ticket.

The following where mentioned in #2978 (closed), but the respective patch did not include them:

• For TemplateHaskell: ⟦ ⟧ (MATHEMATICAL _ WHITE SQUARE BRACKET) can be used instead of [| |]
• For Generics: ⦃ ⦄ (_ WHITE CURLY BRACKET) can be used instead of {| |}
• For Arrows: ⦇ ⦈ (Z NOTATION _ IMAGE BRACKET) can be used instead of (| |)

Generic classes have since been removed and banana brackets were suggested in #10162 (closed) and implemented in D2012, leaving TH quotes.