DeployQt4: Fix usage of BundleUtilities

Due to CMP0080, BundleUtilities can no longer be included at configure-time. However, DeployQt4 contains some functions which are meant to be used at configure-time, and some which are meant to be used at install-time and use BundleUtilities. This change breaks the file into two sections: common functions and install-time functions. BundleUtilities is now only included at install-time, thus fixing the policy warning.

Fixes #18466 (closed).