This commit extracts some common bootstrap rules used for textarea
elements in settings (both organization and stream settings) and
this rules are added for settings_textarea class. We also add
settings_textarea class to the textarea elements in settings.
This change is done so we can safely remove textarea CSS rules
for bootstrap.css as a part of our process to remove bootstrap
without changing existing design.
This lets us provide a hook to where we've written some advice both on
what makes a good stream description, and also what Markdown formatting
is supported there.
Fixes#23376.
We do following changes in this commit to have a uniform file
structure for stream setting templates.
* Move change_stream_info_modal.hbs to stream_settings folder.
* Rename subscription_stream_privacy_modal.hbs to
stream_privacy_setting_modal.hbs.
* Move stream_privacy_setting_modal.hbs to stream_settings folder.