Delegate keyword arguments in Prawn::View#method_missing

Come Ruby 3.x, keyword arguments will not be part of `*arguments` any more. We could either:

1. Mark the method with `ruby2_keywords`, which would make keyword arguments part of `*arguments` again. However, this is going away in the future so it's a crutch if anything.
2. Make the method properly support keyword arguments.

Option 2 is chosen here.

lib/prawn/view.rb

@@ -69,10 +69,10 @@ def document
 
     # Delegates all unhandled calls to object returned by +document+ method.
     # (which is an instance of Prawn::Document by default)
-    def method_missing(method_name, *arguments, &block)
+    def method_missing(method_name, *args, **kwargs, &block)
       return super unless document.respond_to?(method_name)
 
-      document.public_send(method_name, *arguments, &block)
+      document.public_send(method_name, *args, **kwargs, &block)
     end
 
     def respond_to_missing?(method_name, _include_all = false)

spec/prawn/view_spec.rb

@@ -12,12 +12,12 @@
   it 'delegates unhandled methods to object returned by document method' do
     doc = instance_double('Document')
     allow(view_object).to receive(:document).and_return(doc)
-
     allow(doc).to receive(:some_delegated_method)
+    block = proc {}
 
-    view_object.some_delegated_method
+    view_object.some_delegated_method('positional', keyword: 'argument', &block)
 
-    expect(doc).to have_received(:some_delegated_method)
+    expect(doc).to have_received(:some_delegated_method).with('positional', keyword: 'argument', &block)
   end
 
   it 'allows a block-like DSL via the update method' do