feat: experimental Webxdc Integration API, Maps Integration

[r10s]

as discussed in several chats, this PR starts making it possible to use Webxdc as integrations to the main app. In other word: selected parts of the main app can be integrated as Webxdc, eg. Maps ¹

this PR contains two parts:

• draft an Webxdc Integration API
• use the Webxdc Integration API to create a Maps Integration

to be clear: a Webxdc is not part of this PR. the PR is about marking a Webxdc being used as a Map - and core then feeds the Webxdc with location data. from the view of the Webxdc, the normal sendUpdate()/setUpdateListener() is used.

things are still marked as "experimental", idea is to get that in to allow @adbenitez and @nicodh to move forward on the integrations into android and desktop, as well as improving the maps.xdc itself.
good news is that we currently can change the protocol between Webxdc and core at any point :)

Webxdc Integration API

see dc_init_webxdc_integration() in deltachat.h for overview and documentation.

rust code is mostly in webxdc/integration.rs that is called by other places as needed. current user of the API is deltachat-ios, android/desktop will probably follow.

the jsonrpc part is missing and can come in another PR when things are settled and desktop is really starting ² (so we won't need to do all iterations twice :) makes also sense, when this is done by someone actually trying that out on desktop

while the API is prepared to allow other types of integrations (photo editor, compose tools ...) internally, we currently ignore the type. if that gets more crazy, we probably also need a dedicated table for the integrations and not just a single param.

Maps Integration

rust code is mostly in webxdc/maps_integration.rs that is called by webxdc/integration.rs as needed.

EDIT: the idea of having a split here, is that webxdc/maps_integration.rs really can focus on the json part, on the communication with the .xdc, including tests

this PR is basic implementation, enabling to move forward on integrations on iOS, but also on desktop and android.

the current implementation allows already the following:

• global and per-chat maps
• add and display POIs
• show positions and tracks of the last 24 hours

the current maps.xdc uses leaflet, and is in some regards better than the current android/desktop implementations (much faster, show age of positions, fade out positions, always show names of POIs, clearer UI). however, we are also not bound to leaflet, it can be anything

screenshots of the current state
👆

to move forward faster and to keep this PR small, the following will go to a subsequent PR:

• consider allowing webxdc to use a different timewindow for the location
• delete POIs
• jsonrpc

Footnotes

1. maps are a good example as anyways barely native (see android app), did cause a lot of pain on many levels in the past (technically, bureaucratically), and have a comparable simple api ↩

2. only going for jsonrpc would only make sense if large parts of android/ios would use jsonrpc, we're not there ↩

[r10s]

not sure why CI is red suddenly

[Hocuri]

CI is red because of #4476, unrelated to this PR here

[r10s]

although maps for iOS (any maybe other systems) will stay experimental for 1.46, it is still good to get this in to move forward, get experience, bug reports etc. there are things missing pr, see above, but that is on purpose - it is already pretty much reviewed, adding now lots of things does not make much sense

[link2xt]

This is a bit overgeneralized, could have dropped "integration" completely and just name everything "webxdc maps" and merge webxdc::integration and webxdc::maps_integration for now. But otherwise looks good.