compose: Add shortcut hint to New topic and New stream message button.
compose: Add shortcut hint to New topic and New stream message button.

Fixes: #11678.

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