Add new method to Semantics, method_receiver_kind, which returns the kind of self

The options are Shared, Mutable, Consuming, and Copied. Use this to add proper
highlighting to methods based on usage.

crates/hir/src/lib.rs

@@ -38,7 +38,7 @@ pub use crate::{
         Static, Struct, Trait, Type, TypeAlias, TypeParam, Union, VariantDef, Visibility,
     },
     has_source::HasSource,
-    semantics::{original_range, PathResolution, Semantics, SemanticsScope},
+    semantics::{original_range, PathResolution, SelfKind, Semantics, SemanticsScope},
 };
 
 pub use hir_def::{