[Create/edit survey] Allow predefined or free-form data collection in a job, but not both

Summarizing @n-clinton: Having both leads to confusion and complexity in the survey creation process. If users need both, they can create two jobs, one with predefined, one with free-form.

Consequences of this FR:

Web:

* We'd need to add back the "data collection strategy" selector, but with two options instead of three.
* The "Map site" task shown on jobs with "predefined sites" would no longer be conditional - it would always be shown to data collectors for this job.
* There would be no "Map site" option in "free form" data collection jobs.
* Users should be able to duplicate a job to create a parallel "free form" or "predefined" job if they like. They'd then be able to customize the tasks in the job more specifically for each use case.

Android (after https://github.com/google/ground-android/issues/2446):

* It will no longer be possible to add multiple submissions to sites in "free form" jobs; for those, we can show the card when selected but no "add data" affordance. The only way to add data to "free form" jobs is via the "Add site" fab.
* The "Add site" button is only shown if there's at least one "free form" job.
* When "Add site" is tapped, the job selector is shown iff are multiple "Free form" jobs. "Predefined" jobs are not included in the selector.

@vittorino @rawbzz @amegantz FYI