e.g. Playground.
A single file script is like a single function body; the interface of
the file does not affect any other files.
So when a completion happens in a single file script, re-parse the whole
file. But we are still be able to reuse imported modules.
rdar://problem/58378157
If a CC token is right after the '{' we still don't know it's an implicit
getter or a start of a accessor block. Previously, the parser used to
parse it as an accessor block, but it prevents fast-completion kicks in.
Instead handle it as a part of function body parsing so the
fast-completion works.
rdar://problem/58851121
'getEquivalentDeclContextFromSourceFile()' didn't work for accessors
because DeclContext hierarchy and AST hierarhy are not the same.
AST hierarchy:
(TypeDecl or SourceFile) > AbstractStorageDecl > AccessorDecl
DeclContext hierarchy:
(TypeDecl or SourceFile) > AccessorDecl
Handle them specially.
rdar://problem/58632889
