settings_org: Extract get_input_element_value function.
settings_org: Extract get_input_element_value function.

The reason for extracting this function is that getting the text, integer,
boolean value from the input elements (like checkboxes, dropdowns) is a
common task, and later we can use this function to get the input element
value in `settings_notifications` in the upcoming commit.

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