Since this text is only needed for printing a parseable interface during
a non-whole-module build, only put the text inside partial modules. When
we're merging the modules at the end, skip serializing the text.
rdar://44394186
Static properties are not subject to the same restrictions as properties
whose initializers are exposed to clients in @_fixed_layout types.
rdar://45080912
Augment the ASTPrinter to print the name and text of initializer expressions if
a property has an initializer and the type is @_fixed_layout and resides in a resilient module, and serialize the text for partial modules.
With this change, all .swiftinterface files in the project (except for SwiftLang) compile to swiftmodules on macOS.
rdar://43774580
rdar://43812188
