Pass down the installSource to initial scan request

Initiating package will be null and only the source of truth
is InstallRequest. Passing down the install source to scan request.

Test: m PageSizeCompatWarningsTest && atest -c PageSizeCompatWarningsTest
Flag: EXEMPT test_only
Bug: 443089413
Change-Id: Ieec96f2e7319ff15da8aaf483ea2c19c006dd683