fix: Changed name of methods `Blob.from_string()` and `Bucket.from_string()` to `from_uri()`

[holtskinner]

• Other methods use "string" to refer to the actual content of the Blob, not the uri. The updated method name is more intuitive for developers.
• Marked from_string() as deprecated and mapped functionality to from_uri().

Original reasoning for from_string() naming in #7693

[andrewsg]

Thank you!