don't cache parses twice

Before this commit, `Parse`s for original file ended up two times in
salsa's db: first, when we parse original file, and second, when we
parse macro or a file.

Given that parse trees are the worst ofenders in terms of memory, it
makes sense to make sure we store them only once.

crates/ra_hir/src/lib.rs

@@ -60,7 +60,7 @@ pub use self::{
     path::{Path, PathKind},
     name::Name,
     source_id::{AstIdMap, ErasedFileAstId},
-    ids::{HirFileId, MacroDefId, MacroCallId, MacroCallLoc},
+    ids::{HirFileId, MacroDefId, MacroCallId, MacroCallLoc, MacroFile},
     nameres::{PerNs, Namespace, ImportId},
     ty::{Ty, ApplicationTy, TypeCtor, TraitRef, Substs, display::HirDisplay, CallableDef},
     impl_block::{ImplBlock, ImplItem},