Move addNode to FSTCompiler (#12646)

Currently FSTCompiler and FST have circular dependencies to each 
other. FSTCompiler creates an instance of FST, and on adding node 
(add(IntsRef input, T output)), it delegates to FST.addNode() and passes
itself as a variable. This introduces a circular dependency and mixes up 
the FST constructing and traversing code.

To make matter worse, this implies one can call FST.addNode with an 
arbitrary FSTCompiler (as it's a parameter), but in reality it should be 
the compiler which creates the FST.

This commit moves the addNode method to FSTCompiler instead.

Co-authored-by: Anh Dung Bui <[email protected]>

Author: dungba88

lucene/CHANGES.txt

@@ -143,6 +143,7 @@ API Changes
 * GITHUB#12592: Add RandomAccessInput#length method to the RandomAccessInput interface. In addition deprecate
   ByteBuffersDataInput#size in favour of this new method. (Ignacio Vera)
 
+* GITHUB#12646: Move FST#addNode to FSTCompiler to avoid a circular dependency between FST and FSTCompiler
 
 New Features
 ---------------------