Expose new APIs required by Package Installer.

This change contains those constants and methods that were exposed to
@SystemApi or public, with appropriate documentation and permission enforcements.
This allows Package Installer become an updatable module.

Test: atest CtsContentTestCases:PackageManagerTest CtsPackageInstallTestCases:SessionInfoTest CtsPackageInstallTestCases:InstallPromptDetailsTest PackageManagerServiceUnitTests:UninstallCompleteCallbackTest CtsPackageUninstallTestCases
Bug: 241139604
Bug: 239722738
Change-Id: I938d87fc266ff4268aa3fef1cd1405c1598d5ca8