feat(calling): extract getCallingBackend logic to resolveCallingBackend and export resolveCallingBackend#5010

gabrielchl wants to merge 4 commits into

webex:nextwebex/webex-js-sdk:nextfrom

gabrielchl:gabrilee/SPARK-814815-export-getCallingBackendgabrielchl/webex-js-sdk:gabrilee/SPARK-814815-export-getCallingBackendCopy head branch name to clipboard