Hi,
"sap-ui-cachebuster" is not a folder which would be physically existing in the folder structure. The cache buster is a functionality of the UI5 server components on Java/ABAP which handles the cache behavior as described in the documentation. It is a virtual part of the path which would be handled by the resource servlet.
In environments where the resource handler is not available (i.e. using sapui5-static version, just the file structure for usage on plain web servers or in Phonegap), the cache buster cnannot be used.
Regards
Andreas