Add latex mappings for subscript < and > (#52980)

Adds new latex mappings `\_<` => `˱` and similar for `>` to complement
the existing `\_=`, `\_+`, `\_-`. Useful for describing set indices in a
variable name like `x˱ᵢ`.

Author: MilesCranmer

stdlib/REPL/src/latex_symbols.jl

@@ -207,6 +207,8 @@ const latex_symbols = Dict(
     "\\_+" => "₊",
     "\\_-" => "₋",
     "\\_=" => "₌",
+    "\\_<" => "˱",
+    "\\_>" => "˲",
     "\\_(" => "₍",
     "\\_)" => "₎",
     "\\_a" => "ₐ",