This is to workaround runtime warning:
(evolution:769567): evolution-util-WARNING **: 12:21:17.882: Failed to
call 'Evo.EnsureMainDocumentInitialized();' function: WebKitJavascriptError:699:
resource:///e-web-view.js:587:32: TypeError: null is not an object
(evaluating 'elems[ii].contentDocument.body')
Mentioned in https://gitlab.gnome.org/GNOME/evolution/-/issues/1041
It used to be a dialog, which was unnecessary. Let it be shown inline,
in the message preview instead. As a side effect, it's easier to copy
information out of it.
All the previews (in Mail, Contacts, Memos and Tasks) stop using
deprecated WebKitGTK+ DOM API through a WebExtension (and its D-Bus
API) and start using the JavaScriptCore API (and JavaScript as such).
This allows to lightweight the WebExtension for the EWebView
significantly, including drop of the D-Bus API of it, fully relying
on the Inter-Process-Communication of WebKitGTK+ itself.
