swift: Error message for obsoleted protocol composition syntax should say "types" instead of "protocols"

The following syntax error is emitted when the parser spots obsoleted protocol composition syntax:

typealias C = protocol<P, Q> // error: 'protocol<...>' composition syntax has been removed; join the protocols using '&'

The problem with this message is that “protocols” is not an accurate or prudent description of the components at this compilation stage:

• Protocol compositions are not limited to protocols.
• A component can be written in terms of a member type, such as a nested typealias.
• The parser has no knowledge of whether the components are legal, namely, whether they really reference protocols or classes.

A more neutral “types” is preferable.