[FIX] core.IconPool: register lazy stub for IconPool methods
[FIX] core.IconPool: register lazy stub for IconPool methods

This is mainly added to fix the undeclared dependency from
sap.m.ImageHelper to sap.ui.core.IconPool. Adding the dependency to
IconPool in sap/m/library.js would have been an alternative solution, 
but ideally, sap/m/library.js shouldn't statically depend on IconPool.
Such a dependency might be added to ImageHelper once a split of
sap/m/library.js has been done.

Change-Id: Ie1200ce7129ea8e125216693ffa14284af395395
BCP: 1880129607
SAP/openui5,cschuff/openui5,cschuff/openui5,cschuff/openui5,SAP/openui5,SAP/openui5,SAP/openui5