feat(didc-js): encode and validate specific types and service args

[olaszakos]

Overview
This PR extends the didc-js wasm module with capability to encode values of specific types, and values for the service arguments, with the purpose of also validating them against those types. This is useful for JS clients where the user is expected to produce valid candid value for a particular type.

Requirements

• the encode function can receive type information other than service_method such as a type name or instruction to use the service argument types

Considered Solutions
I did not find any other solution.

Recommended Solution
Since encode already has this functionality to encode (and validate) service method arguments, this seems like a good place to extend the functionality.

Considerations