adapt to new saved-messages api

[r10s]

since PR deltachat/deltachat-core-rust#5606 we have a new saved-messages-api, allowing to save messages similar as known from whatsapp or telegram. see that PR for reasonings and discussions.

to benefit from the new saved-messages-api on desktop, the following steps are needed:

• make dc_save_msgs(), dc_msg_get_original_msg_id() and dc_msg_get_saved_msg_id() available in jsonrpc

• in self-chat, for incoming messages, show group avatar, sender name and correct left/right side bubbles and colors, see eg. deltachat/deltachat-android@75e9984 for how to change the condition.
  already now, the state is not that bad: messages from others saved eg. on android are shown on desktop on the left side using the correct color already today, only avatar and sender name is missing

• when forwarding a message to "Saved Messages" that was not already saved use dc_save_msgs() ^{1 2}

• for every message shown in a chat, check if it was saved ³. if so, show a little bookmark icon beside the date (screenshot). as the bookmark should also be shown in saved messages, you will draw it if original_msg_id() OR saved_msg_id() is true.

• add a button to go to original beside each saved message in the self-chat (screenshot)

to get the idea, it makes sense to use iOS or Android 1.54

as the new core is already shipped, there is not a huge urgency to target this issue, no messages saved on iOS/android will be lost or so. but of course, it is a very nice to have adaption, and comparable simple for UI.

Footnotes

1. when a message was already saved, and is forwarded again to "Saved Messages". keep using dc_forward_msgs() - this is to have an option in rare cases when multi-device do not have the message to save. this is also how telegram works ↩

2. in a subsequent PR, we can consider to add a "save/unsave" option directly to the context menu or so, like on iOS ↩

3. at least for the first iteration, we do not want to show saved info messages and thelike in the "Saved Messages" chat; this turned out to be confusing and might also require adaptions on systems other than android (remember: saved messages are synced), cmp. https://github.com/deltachat/deltachat-ios/issues/2567 ↩

[r10s]

closing this for a few days until android is done, a few things are still under discussion

[r10s]

reopend and adapted. recent changes:

• the icons should be a "bookmark icon", screenshot and reasoning
• saving should be possible also by "Forward to saved" as before, to close this issue, this is sufficient. a shortcut, as eg. a "save" context menu entry or so can come in another PR