[firebase_storage] Replace async get methods with simple getters

[awhitford]

One challenge using StorageReference is the async methods for getters like:

• getBucket
• getPath
• getName

Another confusion is getPath vs path -- they seem to respond with the same information, yet the getPath is asynchronous.

Should getPath be deprecated in favor of path?

If a Storage Reference is a URI, why can't simple URI parsing replace these asynchronous methods. For example:

Async Method	URI Equivalent
getBucket	uri.host
getPath	uri.path
getName	uri.pathSegments.last