Fix errors in documentation for Function::callWithThis

Summary:
The documentation in two out of the three variants of `Function::callWithThis` incorrectly stated that the `this` value was to be `undefined` instead of set to `jsThis`, which contradicts the point of the `callWithThis` method existing in the first place. This diff fixes that issue.

Changelog: [General] [Fixed] - Fix documentation comments for HermesJS's `Function::callWithThis` method to accurately reflect how `this` is handled.

Reviewed By: jbower-fb

Differential Revision: D19714074

fbshipit-source-id: 123688c1f7e578d6356bec54604fb6e30f06b0b1

Author: Kronopath

ReactCommon/jsi/jsi/jsi.h

@@ -52,8 +52,8 @@ class StringBuffer : public Buffer {
   std::string s_;
 };
 
-/// PreparedJavaScript is a base class representing JavaScript which is in a form
-/// optimized for execution, in a runtime-specific way. Construct one via
+/// PreparedJavaScript is a base class representing JavaScript which is in a
+/// form optimized for execution, in a runtime-specific way. Construct one via
 /// jsi::Runtime::prepareJavaScript().
 /// ** This is an experimental API that is subject to change. **
 class PreparedJavaScript {
@@ -827,24 +827,22 @@ class Function : public Object {
   Value call(Runtime& runtime, Args&&... args) const;
 
   /// Calls the function with \c count \c args and \c jsThis value passed
-  /// as this value.
+  /// as the \c this value.
   Value callWithThis(
       Runtime& Runtime,
       const Object& jsThis,
       const Value* args,
       size_t count) const;
 
   /// Calls the function with a \c std::initializer_list of Value
-  /// arguments. The \c this value of the JS function will be
-  /// undefined.
+  /// arguments and \c jsThis passed as the \c this value.
   Value callWithThis(
       Runtime& runtime,
       const Object& jsThis,
       std::initializer_list<Value> args) const;
 
   /// Calls the function with any number of arguments similarly to
-  /// Object::setProperty().  The \c this value of the JS function
-  /// will be undefined.
+  /// Object::setProperty(), and with \c jsThis passed as the \c this value.
   template <typename... Args>
   Value callWithThis(Runtime& runtime, const Object& jsThis, Args&&... args)
       const;