Modifies the core package and literal handling to use factory functions
for standard type literals.
Updates function/builtin/import.carbon to stop depending on the prelude,
since it would list all the impls in the core file. Updates
alias/builtins.carbon to be failing (the type values cannot be aliased).
Change syntax for package declaration to put the `impl` keyword at the
start and remove the `api` keyword.
To support this, rearrange processing of package, library, and import
declarations to use the general modifier handling support in declaration
parsing rather than special-case logic.
There is an ambiguity in `impl package.Foo as Bar`, which we resolve by
treating `package` as an introducer after a modifier only if it's not
followed by `.`.
This is modeled analogously to FunctionType. So far, GenericClassType
has no operations, but eventually values of that type will be callable
like values of FunctionType.
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Co-authored-by: Jon Ross-Perkins <jperkins@google.com>
Jon Ross-Perkins
Richard Smith
