Some editors use diagnostics from SourceKit to replace build issues. This causes issues if the diagnostics from SourceKit are formatted differently than the build issues. Make sure they are rendered the same way, removing most uses of `DiagnosticsEditorMode`.
To do so, always emit the `add stubs for conformance` note (which previously was only emitted in editor mode) and remove all `; add <something>` suffixes from notes that state which requirements are missing.
rdar://129283608
Previously, missing return diagnostics for unreachable subscripts
differed from the treatment unreachable functions received, leading to
inconsistent diagnostic behavior. This change removes the responsibility
for handling the relevant diagnostics from the AST code, in favor of the
diagnostics implemented via the SIL optimizer. Additionally, where the
AST-generation code would previously have diagnosed a missing return for
an implicit empty getter, it will now admit as valid, deferring the
missing return diagnostics to the later SIL passes.
This commit changes fixit messages from a question/suggestion to an
imperative message for protocol conformances and switch-case. Addresses
https://github.com/apple/swift/issues/67510.
