This commit is a part of the efforts to rename btn-related classes
and variables to align with Zulip's no-abbreviations policy and
streamline the search results.
This commit renames "dialog_cancel_button" class in the exit button
of modals to "dialog_exit_button", which seems a much better name
for a button that is used to close a modal.
This commit extracts html for modal used for changing email
address visibility during registration to a separate file
so that we can avoid code duplication when we add commits
to allow changing email address visibility for imported
users during login.
Sayam Samal
Sahil Batra