Unfortunately, what you want doesn't exist — there are no system APIs (private or otherwise) that will let you embed Xcode functionality in the way that you want. However, you can take a look at tools like SourceKitten (a wrapper around the SourceKit service that does the syntax highlighting and semantic parsing for Xcode) to replicate some of that yourself.
Depending on what you're looking for and the type of IDE that you want to implement, there are embeddable versions of other editors (say, vim, via the embeddable frameworks that projects like vimr provide) which can provide syntax highlighting and some compilation, but then you're coupling yourself to those editors, how they work, and the features they provide.