The API digester tests were being run only for macOS, mainly
because they were not using %target-swift consistently. Lift
the unnecessary restriction so we run these tests more widely.
This change introduces a Json format change where we always print fully
qualified type names everywhere. This is beneficial for diagnosing purposes but
may not be ideal for generating migrator scripts. To resolve this conflict, the
patch also introduces a flag -migrator to opt-out fully qualified type names.
After the format change, we need to update the ABI and API baselines for the
Swift stdlib.
* swift-api-digester: Add a test for generating migrator script.
* swift-api-digester: Add #ifndef guard before each macro category.
* swift-api-digester: Avoid printing macro categories with empty content.
* swift-api-digester: Add test for multiple type changes in a single decl.
* swift-api-digester: simplify some code. NFC
