(cherry picked from commit a1b56e4a)

These shortcuts still assume they are activating GtkMenuButtons that no
longer exist.

Fixes #2435

Part-of: <https://gitlab.gnome.org/GNOME/epiphany/-/merge_requests/1610>

If the web app icon is a relative path, we append the path to the
current page's URL, creating a path that looks like e.g.:

https://gitlab.gnome.org/GNOME/epiphany/-/issues/2436/-/pwa-icons/logo-512.png

from example path /-/pwa-icons/logo-512.png. But the path is supposed to
be relative to the manifest URL, not the current page.

Fixes #2436

Part-of: <https://gitlab.gnome.org/GNOME/epiphany/-/merge_requests/1613>

Web apps are single tab/window, so accessing the overview shouldn't be
an option.

Closes #2443

Part-of: <https://gitlab.gnome.org/GNOME/epiphany/-/merge_requests/1614>

Because the check button wasn't centered vertically, the focus border
didn't match the shape of the button.

Part-of: <https://gitlab.gnome.org/GNOME/epiphany/-/merge_requests/1618>

This reverts commit 0f1c2715.

Part-of: <https://gitlab.gnome.org/GNOME/epiphany/-/merge_requests/1620>

If the destination string is more than NAME_MAX bytes, then the download
fails. Truncating it fixes the issue.

Closes #2268

Ensure multibyte characters don't get cut off

Uses g_utf8_substring to make sure that truncation doesn't happen in the
middle of a multibyte character.

Convert bytes to characters for g_utf8_substring

To make sure truncation happens at the correct spot, g_utf8_substring
needs to get the number of characters rather than the number of bytes.

Stop untruncated destination filename from leaking

Fix memory leaks

Fix repeatedly downloading long files

(n) is now correctly appended to long filenames rather than getting
overwritten if the filename is too long.

Minor tweaks

Uses g_steal_pointer for a small optimization and fixes a code style
issue.

Part-of: <https://gitlab.gnome.org/GNOME/epiphany/-/merge_requests/1612>

(cherry picked from commit 53ba335f24cd709e84ff2da05d299137bbce6f65)

Part-of: <https://gitlab.gnome.org/GNOME/epiphany/-/merge_requests/1617>

Now that we have AdwTabOverview, it's possible to have no tabs after
Epiphany has started. Got to add a few more checks for this situation.
Notably, this fixes opening a new tab with Ctrl+T and opening links from
external applications if the tab overview is open with zero tabs.

Fixes #2448

Part-of: <https://gitlab.gnome.org/GNOME/epiphany/-/merge_requests/1617>

This cannot be localized properly. Plurals require ngettext().

Fixes #2454

Part-of: <https://gitlab.gnome.org/GNOME/epiphany/-/merge_requests/1619>