Update yarv compiler and decompiler to stop using Elsif node

Author: egiurleo

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),

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