Allow launching applications not pre-declared in ComputerControlSession.

The `launchApplication` API in `ComputerControlSession` no longer requires the package name to be included in `getTargetPackageNames()` at session creation. Instead, when `computerControlActivityPolicyStrict` is enabled, the service dynamically adds an activity policy exemption for the launched package. This is a temporary change to support a broader range of applications until a per-app consent model is implemented. The documentation is updated to reflect that an `IllegalArgumentException` is thrown if the package lacks a launcher activity.

Bug: 444600407
Flag: android.companion.virtualdevice.flags.computer_control_activity_policy_strict
Test: presubmit
Change-Id: I6e87641075f205c4b2b39042f8b53febe9cee6d8