api!(deltachat-jsonrpc): use kind as a tag for all union types

[link2xt]

Closes #4601

[link2xt]

I have tried to change MuteDuration declaration to this:

#[derive(Clone, Serialize, Deserialize, TypeDef, schemars::JsonSchema)]
#[serde(tag = "kind")]
pub enum MuteDuration {
    NotMuted, 
    Forever,
    Until(i64),
}

It results in this OpenRPC specification:

[{'properties': {'kind': {'enum': ['NotMuted'], 'type': 'string'}},
  'required': ['kind'],
  'type': 'object'},
 {'properties': {'kind': {'enum': ['Forever'], 'type': 'string'}},
  'required': ['kind'],
  'type': 'object'},
 {'format': 'int64',
  'properties': {'kind': {'enum': ['Until'], 'type': 'string'}},
  'required': ['kind'],
  'type': ['object', 'integer']}]

'type': ['object', 'integer'] looks weird.

Generated TypeScript type is this:

export type MuteDuration=({"kind":"NotMuted";}|{"kind":"Forever";}|({"kind":"Until";}&I64));

({"kind":"Until";}&I64) seems like an empty type? This question confirms:
https://stackoverflow.com/questions/65908355/why-is-it-allowed-to-intersect-primitives-and-objects-in-typescript

I am going to change the type to have no anonymous fields so this does not happen, but also reported a bug at dbeckwith/rust-typescript-type-def#24

[link2xt]

There is a scripts/generate_openrpc_bindings.py which calls deltachat-rpc-server --openrpc and generates some Python code.

There are some weird types remaining, all involving maps, for example:

• {'type': 'object', 'additionalProperties': {'type': 'string'}} for BTreeMap<&'static str, String>, the return type of get_system_info()
• {'type': 'object', 'additionalProperties': {'type': ['string', 'null']}} for HashMap<String, Option<String>>, the return type of batch_get_config()
• {'type': 'object', 'additionalProperties': {'type': 'string'}} for HashMap<u32, String>, the argument of set_stock_strings
• {'type': 'object', 'additionalProperties': {'$ref': '#/components/schemas/MessageLoadResult'}} for HashMap<u32, MessageLoadResult>, the return type of get_messages

In Reactions there is a field reactions_by_contact, it has this type:

{'additionalProperties': {'items': {'type': 'string'}, 'type': 'array'},
 'description': "Map from a contact to it's reaction to message.",
 'type': 'object'

The problem is that the key of the map is nowhere to be found, it's a bug in yerpc or its dependencies probably. Worst case we have to replace these types with a list of tuples.

Once this is fixed the parser is ready and the remaining part is generating the code to serialize/deserialize arguments and results.

I opened an upstream issue at GREsau/schemars#235

[link2xt]

I have merged this change as no other type changes are needed.
JSON-RPC bindings generator is moved to #4603