desktop: deep links on macOS, Windows and Linux (#7605)

* tests: close the walk stream in withTempDir

* desktop: receive app links from args and macOS

* desktop: forward an app link to the running app

* desktop: initialize the desktop platform lazily

* tests: share the temp directory helper

* desktop: register simplexchat scheme in packages

* desktop: register simplexchat scheme at runtime

* ui: end the badge page with a link on desktop

* desktop: raise the window over other apps

* docs: describe desktop deep links in the spec

* docs: plan desktop deep links

* docs: report on desktop deep links

* desktop: open simplex connection links

* docs: describe simplex links on desktop

* desktop: keep a link from opening twice

* desktop: retry taking a signal held open

* desktop: keep the user's AppImage link handler

* desktop: register Windows links through Capabilities

* desktop: add %u to the deb entry only once

* docs: describe the review fixes

* ui: open the badge link screen on the left

* ui: import moko accessors in the badge screens

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Co-authored-by: spaced4ndy <8711996+spaced4ndy@users.noreply.github.com>

scripts/flatpak/chat.simplex.simplex.desktop

@@ -8,3 +8,4 @@ Categories=Utility;Chat;InstantMessaging;
 Exec=simplex %U
 Icon=chat.simplex.simplex
 StartupWMClass=simplex-chat
+MimeType=x-scheme-handler/simplexchat;x-scheme-handler/simplex;