Auto merge of #16394 - mckaymatt:line_num_offset__issue_15693, r=SimonSapin

Support line number offsets for inline stylesheets

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This allows accurate line numbers when reporting stylesheet errors.

@jdm This is going to require some effort to merge my changes with other recent changes to `ParserContext`. Because of that I would appreciate a quick sanity check before I put the time into performing the merge.
For example, should I store the `offset` as a u64, or should it be an Option?

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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #15693 (github issue number if applicable).

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- [ ] These changes do not require tests because _____

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components/script/dom/htmlstyleelement.rs

@@ -40,6 +40,7 @@ pub struct HTMLStyleElement {
     in_stack_of_open_elements: Cell<bool>,
     pending_loads: Cell<u32>,
     any_failed_load: Cell<bool>,
+    line_number: u64,
 }
 
 impl HTMLStyleElement {
@@ -55,6 +56,7 @@ impl HTMLStyleElement {
             in_stack_of_open_elements: Cell::new(creator.is_parser_created()),
             pending_loads: Cell::new(0),
             any_failed_load: Cell::new(false),
+            line_number: creator.return_line_number(),
         }
     }
 
@@ -92,7 +94,8 @@ impl HTMLStyleElement {
         let loader = StylesheetLoader::for_element(self.upcast());
         let sheet = Stylesheet::from_str(&data, win.get_url(), Origin::Author, mq,
                                          shared_lock, Some(&loader),
-                                         win.css_error_reporter());
+                                         win.css_error_reporter(),
+                                         self.line_number);
 
         let sheet = Arc::new(sheet);