Rust: Fix grammar and add documentation comments

Author: paldepind

rust/ql/lib/codeql/rust/controlflow/internal/Scope.qll

@@ -7,8 +7,10 @@ private import codeql.rust.elements.internal.generated.ParentChild
  * A control-flow graph (CFG) scope.
  */
 abstract private class CfgScopeImpl extends AstNode {
+  /** Holds if `first` is executed first when entering `scope`. */
   abstract predicate scopeFirst(AstNode first);
 
+  /** Holds if `scope` is exited when `last` finishes with completion `c`. */
   abstract predicate scopeLast(AstNode last, Completion c);
 }
 

rust/ql/lib/codeql/rust/elements/AsyncBlockExpr.qll

@@ -1,7 +1,11 @@
+/**
+ * This module provides the public class `AsyncBlockExpr`.
+ */
+
 private import codeql.rust.elements.BlockExpr
 
 /**
- * A async block expression. For example:
+ * An async block expression. For example:
  * ```rust
  * async {
  *     let x = 42;