In a following diff, I want to use this constant from lib/keyserver-conn/recovery-utils.js. Since that file already imports from keyserver-connection-handler.js, this has the risk of introducing an import cycle. To preempt that I decided to extract the constant to a types file.
I also snuck in an unrelated minor change: I replaced the export at the end of keyserver-conn-types.js with individual export lines at the declarations, to make the style consistent throughout the file.
Depends on D11220