PICKME: Ensure that nodes are correctly processed in HTML content

This condition:

> Reprocess the token according to the rules given in the section
> corresponding to the current insertion mode in HTML content.

Was resulting in an infinite loop in fragment cases. In full documents,
after popping nodes the context is always moved so that foreign content
parsing is not used. This is not guaranteed in a fragment and could
cause an infinite loop.

Author: sirreal

src/wp-includes/html-api/class-wp-html-processor.php

@@ -4557,7 +4557,7 @@ private function step_in_foreign_content(): bool {
 
 					$this->state->stack_of_open_elements->pop();
 				}
-				return $this->step( self::REPROCESS_CURRENT_NODE );
+				goto in_foreign_content_process_in_current_insertion_mode;
 		}
 
 		/*
@@ -4633,6 +4633,7 @@ private function step_in_foreign_content(): bool {
 				goto in_foreign_content_end_tag_loop;
 			}
 
+			in_foreign_content_process_in_current_insertion_mode:
 			switch ( $this->state->insertion_mode ) {
 				case WP_HTML_Processor_State::INSERTION_MODE_INITIAL:
 					return $this->step_initial();