When starting Epiphany, we load an empty HTML document in all tabs
except the currently-presented tab in order to start quickly and avoid
excess memory usage. The real document is loaded later when the user
clicks on the tab for the first time after starting the browser. But
there's a problem with this strategy: if the user never clicks on the
tab, then the placeholder document is still there when we quit, and we
accidentally save the *placeholder* into the session state instead of
the real state of the tab that was restored from the previous session.
The most obvious impact of this is you lose the contents of the
back/forward list.

This fixes the issue by ensuring we check to see if delayed session
state is available when saving the session. If so, the web view is
displaying a placeholder document and we want to save the delayed state,
not the placeholder state.

Fixes #1622

Part-of: <https://gitlab.gnome.org/GNOME/epiphany/-/merge_requests/1191>

ephy_web_extension_manifest_get_localized_string() will now never
return NULL.

Part-of: <https://gitlab.gnome.org/GNOME/epiphany/-/merge_requests/1189>

We already do it in ephy_window_close_tab().

Part-of: <https://gitlab.gnome.org/GNOME/epiphany/-/merge_requests/1188>

We never set it to anything but null, but also clear weak pointer.

Part-of: <https://gitlab.gnome.org/GNOME/epiphany/-/merge_requests/1188>

The latter has a way to get EphyTabView from it; if EphyTabView is disposed
first, we get a use-after-free.

Part-of: <https://gitlab.gnome.org/GNOME/epiphany/-/merge_requests/1188>

As of https://gitlab.gnome.org/GNOME/adwaita-icon-theme/-/commit/c19295d8848bd360313cef14fbf9a1d59a483962
non-starred-symbolic is partially transparent and looks insensitive where
we use it. Bundle the old version and use it instead.

Part-of: <https://gitlab.gnome.org/GNOME/epiphany/-/merge_requests/1185>

This partially reverts 73c4fb03.
We don't want Meson checking to ensure the command succeeds because we
handle failure immediately below. Oops.

Meson complains the older versions are deprecated.

Meson complains that this is deprecated.

This avoids whining from Meson, see:
https://github.com/mesonbuild/meson/issues/9300

and is surely a good idea in general.

When importing bookmarks, we have:

 (1) EphyWindow, transient parent of
 (2) GtkDialog to select where to import bookmarks from, transient
parent of
 (3) The native file chooser dialog (in case of GVDB or HTML import)

Sadly, opening a native dialog on a modal dialog hangs the application,
gtk#5011. To dodge this problem, we can close the second dialog
dialog when opening the third dialog, and make the EphyWindow the
transient parent of the third dialog. This is inconvenient because it
means you're all the way back to step one if you decide to cancel the
third dialog and want to go back to the second dialog, but it's better
than a hang.

Exporting bookmarks does not have this problem, because there we skip
step 2.

Importing passwords does not have this problem, because there we don't
have a native file chooser. (At least, I think so. Didn't test this
because I do not have Chrome installed.)