[Flang] Update Extensions.md for supported BIND(C) LOGICAL kind.

[DanielCChen]

Flang also supports non-scalar logical dummy argument with a different KIND from C_BOOL to a bind(c) routine as well as a component in a bind(c) derived type. Update the document.

subroutine sub(arg)
logical(4) :: arg(4)
end

type dt
logical(4) :: comp
end type
end

[DanielCChen]

Thanks for the review!