Comment 1 for bug 1765442

This is deliberate. From debian:changelog:

"Rename binary packages to match upstream library naming scheme"

and

https://launchpad.net/ubuntu/bionic/amd64/libqt5scintilla2-designer/2.10.2+dfsg-4

"This is a dummy transitional package provided to support upgrades."

Depends on: libqscintilla2-qt5-designer

https://packages.ubuntu.com/bionic/amd64/libqscintilla2-qt5-designer/filelist