Break long method definitions when auto-correcting

This allows rubocop to autocorrect method definitions by wrapping them
on multiple lines when they violate the `Layout/LineLength` rule by
adding method definition logic inside `CheckLineBreakable`.

changelog/new_autocorrect_wraps_method_definitions.md

@@ -0,0 +1 @@
+* [#10692](https://github.com/rubocop/rubocop/pull/10692): Break long method definitions when auto-correcting. ([@Korri][])

lib/rubocop/cop/layout/line_length.rb

@@ -80,6 +80,7 @@ def on_potential_breakable_node(node)
         alias on_array on_potential_breakable_node
         alias on_hash on_potential_breakable_node
         alias on_send on_potential_breakable_node
+        alias on_def on_potential_breakable_node
 
         def on_new_investigation
           check_for_breakable_semicolons(processed_source)

lib/rubocop/cop/mixin/check_line_breakable.rb

@@ -46,6 +46,8 @@ def extract_breakable_node(node, max)
         if node.send_type?
           args = process_args(node.arguments)
           return extract_breakable_node_from_elements(node, args, max)
+        elsif node.def_type?
+          return extract_breakable_node_from_elements(node, node.arguments, max)
         elsif node.array_type? || node.hash_type?
           return extract_breakable_node_from_elements(node, node.children, max)
         end
@@ -216,6 +218,8 @@ def process_args(args)
 
       # @api private
       def already_on_multiple_lines?(node)
+        return node.first_line != node.arguments.last.last_line if node.def_type?
+
         node.first_line != node.last_line
       end
     end

spec/rubocop/cop/layout/line_length_spec.rb

@@ -597,6 +597,32 @@ def method_definition_that_is_just_under_the_line_length_limit(foo) # rubocop:di
       end
     end
 
+    context 'method definition' do
+      context 'when under limit' do
+        it 'does not add any offenses' do
+          expect_no_offenses(<<~RUBY)
+            def foo(foo: 1, bar: "2"); end
+          RUBY
+        end
+      end
+
+      context 'when over limit' do
+        it 'adds an offense and autocorrects it' do
+          expect_offense(<<~RUBY)
+            def foo(abc: "100000", def: "100000", ghi: "100000", jkl: "100000", mno: "100000")
+                                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Line is too long. [82/40]
+            end
+          RUBY
+
+          expect_correction(<<~RUBY)
+            def foo(abc: "100000", def: "100000",#{trailing_whitespace}
+            ghi: "100000", jkl: "100000", mno: "100000")
+            end
+          RUBY
+        end
+      end
+    end
+
     context 'method call' do
       context 'when under limit' do
         it 'does not add any offenses' do