docs: Add documentation for tab switcher.
docs: Add documentation for tab switcher.

Documentation for tab switcher added under User documentation
features as a section at the bottom of "Tips and Warnings" article.

Text substantially rewritten by tabbott.

Fixes #12505

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