Update yarv compiler and decompiler to stop using Elsif node

Author: egiurleo

Diff for: CHANGELOG.md

@@ -17,6 +17,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/) a
 
 - Fixed the AST output by adding blocks to `Command` and `CommandCall` nodes in the `FieldVisitor`.
 - Fixed the location of lambda local variables (e.g., `->(; a) {}`).
+- The `Elsif` node has been folded into `IfNode`. A `keyword` field has been added to `IfNode` specifying if the node represents an `if` or `elsif`.
 
 ## [6.0.1] - 2023-02-26
 

Diff for: lib/syntax_tree/yarv/compiler.rb

@@ -916,17 +916,6 @@ def visit_else(node)
         iseq.pop unless last_statement?
       end
 
-      def visit_elsif(node)
-        visit_if(
-          IfNode.new(
-            predicate: node.predicate,
-            statements: node.statements,
-            consequent: node.consequent,
-            location: node.location
-          )
-        )
-      end
-
       def visit_ensure(node)
       end
 
@@ -1054,6 +1043,7 @@ def visit_if(node)
       def visit_if_op(node)
         visit_if(
           IfNode.new(
+            keyword: Kw.new(value: "if", location: Location.default),
             predicate: node.predicate,
             statements:
               Statements.new(body: [node.truthy], location: Location.default),

Diff for: lib/syntax_tree/yarv/decompiler.rb

@@ -77,7 +77,7 @@ def decompile(iseq)
               Next(Args([]))
             ]
 
-            clause << IfNode(clause.pop, Statements(body), nil)
+            clause << IfNode(Kw("if"), clause.pop, Statements(body), nil)
           when Dup
             clause << clause.last
           when DupHash