Explicitely specify the type of DW_OP_WASM_location values

[pfaffe]

In DWARF v5, values on the DWARF expression stack are typed (see 2.5.1 of [DWARF]). Most of the time the types are implicit and defined by the operation and its operands. In the wasm extension, it's implicitely clear that the result type of a DW_OP_WASM_location is just the type of the local/global/operand being loaded, but perhaps the spec should be more explicit!