Add option to start an app by its name

By adding the '?' prefix, the app is searched by its name instead of its
package name (retrieving app names on the device may take some time):

    scrcpy --start-app=?firefox

An app matches if its label starts with the given name,
case-insensitive.

If '+' is also passed to force-stop the app before starting, then the
prefixes must be in that order:

    scrcpy --start-app=+?firefox

PR #5370 <https://github.com/Genymobile/scrcpy/pull/5370>