Check accessibility of all build{Partial}Block overloads and
diagnose if none of them are as accessible as type, otherwise
swift interfaces could end up with invalid result builder
declarations when type is public and all builder methods are
internal.
Resolves: rdar://104384604
Custom attributes were not printed because they are marked
'UserInaccesible'.
* Make CustomAttr 'RejectByParser' instead of 'UserInaccessible'
* Remove special treatment for Result Builder attributes
* Load implicit modules in module/header interface gen requests
rdar://79927502
"Function builders" are being renamed to "result builders". Add the
corresponding `@resultBuilder` attribute, with `@_functionBuilder` as
an alias for it, Update test cases to use @resultBuilder.
Otherwise we can get in trouble when a local type is named, say,
'Sequence'.
Also contains test updates and a fix for Harlan's previous commit,
which actually affects all typealiases, not just those in the Builtin
module.
The recovery logic was erronously kicking in, because it was comparing
the substituted underlying type with the declaration's underlying type.
For a generic typealias, these never equal, so instead, serialize the
unsubstituted type, and substitute it in deserialization.
