Split Prism::Loader#load_node in one lambda per node type

* Otherwise load_node is too big to compile and is forced to run in interpreter:
  oracle/truffleruby#3293 (comment)
* For the benchmark at oracle/truffleruby#3293 (comment)
  TruffleRuby Native 23.1.0:
  Before: 10.574041 After: 5.592436
  JRuby 9.4.3.0:
  Before: 7.037780 After: 3.995317
  JRuby 9.4.3.0 -Xcompile.invokedynamic=true:
  Before: 7.047832 After: 2.269294

templates/lib/prism/serialize.rb.erb

@@ -47,6 +47,7 @@ module Prism
         @constant_pool = nil
 
         @source = source
+        define_load_node_lambdas
       end
 
       def load_encoding
@@ -196,31 +197,36 @@ module Prism
 
       def load_node
         type = io.getbyte
-        location = load_location
-
-        case type
-        <%- nodes.each_with_index do |node, index| -%>
-        when <%= index + 1 %> then
-          <%- if node.needs_serialized_length? -%>
-          load_serialized_length
+        @load_node_lambdas[type].call
+      end
+
+      def define_load_node_lambdas
+        @load_node_lambdas = [
+          nil,
+          <%- nodes.each do |node| -%>
+          -> {
+            location = load_location
+            <%- if node.needs_serialized_length? -%>
+            load_serialized_length
+            <%- end -%>
+            <%= node.name %>.new(<%= (node.fields.map { |field|
+              case field
+              when Prism::NodeField then "load_node"
+              when Prism::OptionalNodeField then "load_optional_node"
+              when Prism::StringField then "load_string"
+              when Prism::NodeListField then "Array.new(load_varint) { load_node }"
+              when Prism::ConstantField then "load_required_constant"
+              when Prism::OptionalConstantField then "load_optional_constant"
+              when Prism::ConstantListField then "Array.new(load_varint) { load_required_constant }"
+              when Prism::LocationField then "load_location"
+              when Prism::OptionalLocationField then "load_optional_location"
+              when Prism::UInt32Field, Prism::FlagsField then "load_varint"
+              else raise
+              end
+            } + ["location"]).join(", ") -%>)
+          },
           <%- end -%>
-          <%= node.name %>.new(<%= (node.fields.map { |field|
-            case field
-            when Prism::NodeField then "load_node"
-            when Prism::OptionalNodeField then "load_optional_node"
-            when Prism::StringField then "load_string"
-            when Prism::NodeListField then "Array.new(load_varint) { load_node }"
-            when Prism::ConstantField then "load_required_constant"
-            when Prism::OptionalConstantField then "load_optional_constant"
-            when Prism::ConstantListField then "Array.new(load_varint) { load_required_constant }"
-            when Prism::LocationField then "load_location"
-            when Prism::OptionalLocationField then "load_optional_location"
-            when Prism::UInt32Field, Prism::FlagsField then "load_varint"
-            else raise
-            end
-          } + ["location"]).join(", ") -%>)
-          <%- end -%>
-        end
+        ]
       end
     end