Add version validation to cmExportPackageInfoGenerator. Specifically, if
a package uses the "simple" version schema (which is the default if no
schema is specified), validate that the specified version actually
conforms to the schema and issue an error if it does not. Also, issue a
warning if the schema is not recognized.
`include-what-you-use` diagnostics, in practice, are specific to
the environment's compiler and standard library. Update includes
to satisfy IWYU for our CI job under Debian 13. Some patterns:
* Types named in virtual `override` signatures no longer require
includes since the overridden signature already names them.
* A function argument's type needs to be included even if its constructor
is called only by implicit conversion. For example, constructing a
`std::function` from a lambda now requires `<functional>`.
* Some prior mysterious `<type_traits>` inclusions are no longer required.
CPS package metadata involves a fair amount of passing around a
particular set of values, as well as shared argument handling, which is
only going to increase as additional features are added. In order to
reduce code duplication (now and going forward), create a helper class
to handle the shared argument parsing and to serve as a container to
pass metadata values.
Matthew Woehlke