Fix errors in documentation for Function::callWithThis
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

myntra/react-native,hammerandchisel/react-native,arthuralee/react-native,javache/react-native,javache/react-native,exponent/react-native,facebook/react-native,hammerandchisel/react-native,janicduplessis/react-native,janicduplessis/react-native,hammerandchisel/react-native,facebook/react-native,hammerandchisel/react-native,myntra/react-native,janicduplessis/react-native,exponentjs/react-native,pandiaraj44/react-native,exponentjs/react-native,hoangpham95/react-native,arthuralee/react-native,hoangpham95/react-native,myntra/react-native,facebook/react-native,myntra/react-native,hoangpham95/react-native,hoangpham95/react-native,facebook/react-native,exponent/react-native,exponentjs/react-native,exponentjs/react-native,facebook/react-native,arthuralee/react-native,janicduplessis/react-native,janicduplessis/react-native,pandiaraj44/react-native,hammerandchisel/react-native,exponentjs/react-native,exponent/react-native,javache/react-native,myntra/react-native,hoangpham95/react-native,myntra/react-native,exponent/react-native,janicduplessis/react-native,pandiaraj44/react-native,arthuralee/react-native,javache/react-native,javache/react-native,exponent/react-native,exponentjs/react-native,hammerandchisel/react-native,pandiaraj44/react-native,facebook/react-native,janicduplessis/react-native,facebook/react-native,arthuralee/react-native,hammerandchisel/react-native,myntra/react-native,facebook/react-native,exponent/react-native,exponent/react-native,javache/react-native,pandiaraj44/react-native,myntra/react-native,myntra/react-native,javache/react-native,exponentjs/react-native,hammerandchisel/react-native,janicduplessis/react-native,javache/react-native,exponent/react-native,hoangpham95/react-native,pandiaraj44/react-native,javache/react-native,facebook/react-native,hoangpham95/react-native,pandiaraj44/react-native,pandiaraj44/react-native,hoangpham95/react-native,exponentjs/react-native