Change linking information for qwebengine_convert_dict

Use convert_dict_linking.pri instead of QtWebEngineCore_linking.pri
for qwebengine_convert_dict linking step. New linking information
contains only required dependencies, so linker should have much
less work to resolve all the symbols.

The target change to executable is also required to
generate convert_dict_linking.pri

Task-number: QTBUG-53135
Change-Id: I1432207bd1853e762d5d8291ce61027592fd0161
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>