Standardise content type handling in MSC3089 createFile() and createNewVersion() (#2014)
* Provide cross platform compatible versions of createFile() and createNewVersion()
The exist implementations are deprecated as they only work in a browser and support a different type of contents from MatrixClient.uploadContent()
* Fix MSC3089 content upload meta data in NodeJS runtime
* Break unstable createFile() and createNewVersion() instead of deprecating
Test using NodeJS types instead of mocked browser Blob
* chore: remove incorrect comment