Implement IF NODE locations

The following Location information has been added This is the information required for parse.y to be a universal parser:

```
❯ ruby --parser=prism --dump=parsetree -y -e "if a; elsif b; else end"
@ ProgramNode (location: (1,0)-(1,23))
+-- locals: []
+-- statements:
    @ StatementsNode (location: (1,0)-(1,23))
    +-- body: (length: 1)
        +-- @ IfNode (location: (1,0)-(1,23))
            +-- if_keyword_loc: (1,0)-(1,2) = "if"
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
            +-- predicate:
            |   @ CallNode (location: (1,3)-(1,4))
            |   +-- CallNodeFlags: variable_call, ignore_visibility
            |   +-- receiver: nil
            |   +-- call_operator_loc: nil
            |   +-- name: :a
            |   +-- message_loc: (1,3)-(1,4) = "a"
            |   +-- opening_loc: nil
            |   +-- arguments: nil
            |   +-- closing_loc: nil
            |   +-- block: nil
            +-- then_keyword_loc: nil
            ^^^^^^^^^^^^^^^^^^^^^^^^^
            +-- statements: nil
            +-- subsequent:
            |   @ IfNode (location: (1,6)-(1,23))
            |   +-- if_keyword_loc: (1,6)-(1,11) = "elsif"
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
            |   +-- predicate:
            |   |   @ CallNode (location: (1,12)-(1,13))
            |   |   +-- CallNodeFlags: variable_call, ignore_visibility
            |   |   +-- receiver: nil
            |   |   +-- call_operator_loc: nil
            |   |   +-- name: :b
            |   |   +-- message_loc: (1,12)-(1,13) = "b"
            |   |   +-- opening_loc: nil
            |   |   +-- arguments: nil
            |   |   +-- closing_loc: nil
            |   |   +-- block: nil
            |   +-- then_keyword_loc: nil
                ^^^^^^^^^^^^^^^^^^^^^^^^^
            |   +-- statements: nil
            |   +-- subsequent:
            |   |   @ ElseNode (location: (1,15)-(1,23))
            |   |   +-- else_keyword_loc: (1,15)-(1,19) = "else"
            |   |   +-- statements: nil
            |   |   +-- end_keyword_loc: (1,20)-(1,23) = "end"
            |   +-- end_keyword_loc: (1,20)-(1,23) = "end"
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
            +-- end_keyword_loc: (1,20)-(1,23) = "end"
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
```

1 files changed, 18 insertions, 0 deletions

diff --git a/test/ruby/test_ast.rb b/test/ruby/test_ast.rb
index edfc25c43d..dcbd8d6b58 100644
--- a/test/ruby/test_ast.rb
+++ b/test/ruby/test_ast.rb
@@ -1376,6 +1376,24 @@ dummy
       assert_locations(node.children[-1].locations, [[1, 0, 1, 17], [1, 0, 1, 4], [1, 14, 1, 17]])
     end
 
+    def test_if_locations
+      node = ast_parse("if cond then 1 else 2 end")
+      assert_locations(node.children[-1].locations, [[1, 0, 1, 25], [1, 0, 1, 2], [1, 8, 1, 12], [1, 22, 1, 25]])
+
+      node = ast_parse("1 if 2")
+      assert_locations(node.children[-1].locations, [[1, 0, 1, 6], [1, 2, 1, 4], nil, nil])
+
+      node = ast_parse("if 1; elsif 2; else end")
+      assert_locations(node.children[-1].locations, [[1, 0, 1, 23], [1, 0, 1, 2], [1, 4, 1, 5], [1, 20, 1, 23]])
+      assert_locations(node.children[-1].children[-1].locations, [[1, 6, 1, 19], [1, 6, 1, 11], [1, 13, 1, 14], [1, 20, 1, 23]])
+
+      node = ast_parse("true ? 1 : 2")
+      assert_locations(node.children[-1].locations, [[1, 0, 1, 12], nil, [1, 9, 1, 10], nil])
+
+      node = ast_parse("case a; in b if c; end")
+      assert_locations(node.children[-1].children[1].children[0].locations, [[1, 11, 1, 17], [1, 13, 1, 15], nil, nil])
+    end
+
     def test_next_locations
       node = ast_parse("loop { next 1 }")
       assert_locations(node.children[-1].children[-1].children[-1].locations, [[1, 7, 1, 13], [1, 7, 1, 11]])