The code completion might occur inside an attriubte that isn’t part of the AST because it’s missing a `VarDecl` that it could be attached to. In these cases, record the `CustomAttr` and type check it standalone, pretending it was part of a `DeclContext`.
This also fixes a few issues where code completion previously wouldn’t find the attribute constructor call and thus wasn’t providing code completion inside the property wrapper.
rdar://92842803
* Re-create `ASTScope` for each completion
* Add generic params and where clause scope even without missing body
* Use `getOriginalBodySourceRange()` for `AbstractFunctionBodyScope`
* Source range translations for replaced ranges when finding scopes
* Bypass source range checks when the completion happens in the replaced
range
* Be lenient with ASTScope / DeclContext mismatch in code completion
Most tests were using %swift or similar substitutions, which did not
include the target triple and SDK. The driver was defaulting to the
host OS. Thus, we could not run the tests when the standard library was
not built for OS X.
Swift SVN r24504
