fix(developer): improve CEF location search stability

Fixes #4278.

When Keyman Developer is installed without Keyman for Windows, the
program silently crashes, because it is looking for libcef.dll in the
Keyman Desktop install folder rather than using its own copy of it.

This improves the search for libcef.dll and kmbrowserhost.exe, and
includes kmbrowserhost.exe with the Keyman Developer installation.

In the future, we could consider moving kmbrowserhost.exe into a common
folder (perhaps when we split Keyman for Windows and Keyman Developer
projects in 15.0).

I threw in a one-liner addressing a deprecated function warning in the
Developer build.