TypeDescriptor information gets lost when applying multiple DoFn on Composite Transform

While working on BEAM-12384 to preserve correctly the typeDescriptor of the Read transform. I noticed that ParDo passes the outputType information into the next transforms by taking the output of `getOutputTypeDescriptor` specified in the `DoFn`, but the subsequent transform does not get the full inputTypeDescriptor.

There are other open questions:
1. How can we make this easier for users who rarely override the getOutputTypeDescriptor?
2. Where the typeDescriptor should come in the SDF case, from the Restriction?

For more details:
https://github.com/apache/beam/pull/14854#issuecomment-848793500

Imported from Jira [BEAM-12420](https://issues.apache.org/jira/browse/BEAM-12420). Original Jira may contain additional context.
Reported by: iemejia.