Use new OTP28.1 :re.import in escaped regex AST

[sabiwara]

Take 2 for #14719.

Leverages :re.import added in erlang/otp#9976.

Here I went for Macro.escape rather than :elixir_expand, because :elixir_expand is harder to work with since we're already in AST land and the AST for a struct is hard to pattern-match on.

This works since Macro.escape is used in ~r, and also fixes the escaping issue discussed previously. But this is violating the assumption that escape emits AST for a literal, which is probably a no-go.

Will work on supporting the :export option separately since this is not strictly needed for this.

[josevalim]

Notes to self: how we're going to check that the __escape__ function is defined?

• function_exported? is not enough because there is no guarantee the struct module will be loaded. For example, module Bar.foo may do %Foo{} which is inlined as a map, so when calling Bar.foo, the Foo module is not loaded
• Code.ensure_loaded? should be enough, however. If there is a struct, then definition its module is available
• Code.ensure_compiled? is problematic, as it can lead to deadlocks in the compiler