`DropdownButton`: Update `selectedItemBuilder` example to show case item alignment and update DropdownButton examples (#102748)

[DropdownButton]: Fix `alignment`parameter doesn't work for `hint` when `isExpanded: true` (#102752)

* Adding two staging tests to ci.yaml

Adding a properties block (linux_stating_build) and 2 builds
that use this to ci.yaml. This is to verify some failures on
these builds that are happening when running via entries
in devicelab_stating_config.star file.

Bug:102406

* Updating staging build entries to use new naming convention

Staging builds now use a name prefix of Staging_build_, which
allows us to filter these builds on the dashboard.

* Moving bringup:true to target level

We can't add bringup:true to properties block level, so
need to move this back to each target.