hotkeys: Add shortcuts for pan and zoom in lightbox view
hotkeys: Add shortcuts for pan and zoom in lightbox view

This commit adds support for '+' and 'Z' for "zoom in" and '-' and 'z'
for "zoom out" shortcut keys in the lightbox image viewer for Pan and
Zoom.

Fixes: #8689.

dhcrzf/zulip,punchagan/zulip,synicalsyntax/zulip,rht/zulip,dhcrzf/zulip,showell/zulip,hackerkid/zulip,hackerkid/zulip,shubhamdhama/zulip,brainwane/zulip,rht/zulip,punchagan/zulip,rht/zulip,zulip/zulip,zulip/zulip,hackerkid/zulip,tommyip/zulip,jackrzhang/zulip,synicalsyntax/zulip,rht/zulip,hackerkid/zulip,showell/zulip,timabbott/zulip,punchagan/zulip,showell/zulip,dhcrzf/zulip,hackerkid/zulip,rishig/zulip,andersk/zulip,showell/zulip,kou/zulip,synicalsyntax/zulip,andersk/zulip,kou/zulip,brainwane/zulip,eeshangarg/zulip,brainwane/zulip,hackerkid/zulip,timabbott/zulip,tommyip/zulip,andersk/zulip,jackrzhang/zulip,brainwane/zulip,timabbott/zulip,andersk/zulip,kou/zulip,kou/zulip,jackrzhang/zulip,rht/zulip,eeshangarg/zulip,jackrzhang/zulip,tommyip/zulip,brainwane/zulip,shubhamdhama/zulip,dhcrzf/zulip,zulip/zulip,brainwane/zulip,andersk/zulip,hackerkid/zulip,showell/zulip,rishig/zulip,zulip/zulip,zulip/zulip,shubhamdhama/zulip,punchagan/zulip,shubhamdhama/zulip,shubhamdhama/zulip,kou/zulip,dhcrzf/zulip,jackrzhang/zulip,rishig/zulip,shubhamdhama/zulip,dhcrzf/zulip,dhcrzf/zulip,andersk/zulip,rishig/zulip,kou/zulip,eeshangarg/zulip,rht/zulip,zulip/zulip,tommyip/zulip,brainwane/zulip,synicalsyntax/zulip,synicalsyntax/zulip,rishig/zulip,eeshangarg/zulip,rishig/zulip,timabbott/zulip,timabbott/zulip,eeshangarg/zulip,zulip/zulip,jackrzhang/zulip,showell/zulip,jackrzhang/zulip,shubhamdhama/zulip,punchagan/zulip,tommyip/zulip,showell/zulip,kou/zulip,rht/zulip,synicalsyntax/zulip,andersk/zulip,eeshangarg/zulip,tommyip/zulip,rishig/zulip,timabbott/zulip,eeshangarg/zulip,synicalsyntax/zulip,timabbott/zulip,punchagan/zulip,punchagan/zulip,tommyip/zulip