servo: Merge #13589 - Support SVG element (from splav:SVGElement#12974); r=pcwalton,Ms2ger

<!-- Please describe your changes on the following line: -->
minimal SVG element implementation
---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #12974 (github issue number if applicable).

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- [x] There are tests for these changes OR
- [ ] These changes do not require tests because _____

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Source-Repo: https://github.com/servo/servo
Source-Revision: dad3b4785a73aa6ddea5ed50ee4ef01bd4049c8d

servo/components/script_layout_interface/lib.rs

@@ -95,6 +95,7 @@ pub enum LayoutElementType {
     HTMLTableRowElement,
     HTMLTableSectionElement,
     HTMLTextAreaElement,
+    SVGSVGElement,
 }
 
 pub struct HTMLCanvasData {
@@ -103,6 +104,11 @@ pub struct HTMLCanvasData {
     pub height: u32,
 }
 
+pub struct SVGSVGData {
+    pub width: u32,
+    pub height: u32,
+}
+
 /// The address of a node known to be valid. These are sent from script to layout.
 #[derive(Clone, PartialEq, Eq, Copy)]
 pub struct TrustedNodeAddress(pub *const c_void);