Handle install-constraints tag.

The tag can only be used by allowed packages. The list of the allowed
packages is controlled by configuration on a device, and it gets parsed
in SystemConfig.

A config is expected to have "install-constraints-allowed" tags per
package:

"""
<config>
    <install-constraints-allowed package="foo" />
    <install-constraints-allowed package="bar" />
</config>
"""

Bug: b/232475788
Test: atest AppSecurityTests com.android.server.systemconfig.SystemConfigTest
Change-Id: If3c07ddc1e58a5d16547a50437c939d17b3a4e69