[LBSE] Not all 'outermost' <svg> elements enforce a stacking context

https://bugs.webkit.org/show_bug.cgi?id=244965

Reviewed by Rob Buis.

Add missing condition in Style::Adjuster::adjustSVGElementStyle() to enforce
a stacking context if the element that receives the style is an outermost
<svg> element (or acts as such). It is mentioned in the SVG2 spec note just
a few lines above, but not implemented yet.

* LayoutTests/platform/mac-monterey-wk2-lbse-text/svg/css/text-shadow-multiple-expected.txt:
* LayoutTests/platform/mac-monterey-wk2-lbse-text/svg/custom/image-parent-translation-expected.txt:
* LayoutTests/platform/mac-monterey-wk2-lbse-text/svg/custom/second-inline-text-expected.txt:
* Source/WebCore/style/StyleAdjuster.cpp:
(WebCore::Style::Adjuster::adjustSVGElementStyle):

Canonical link: https://commits.webkit.org/254314@main

LayoutTests/platform/mac-monterey-wk2-lbse-text/svg/css/text-shadow-multiple-expected.txt

@@ -13,10 +13,6 @@ layer at (0,0) size 800x408
           text run at (0,0) width 567: "The next two texts have subtle differences, as the stroke/fill is painted seperated in SVG."
       RenderBlock (anonymous) at (0,238) size 800x154
         RenderText {#text} at (0,0) size 0x0
-layer at (0,100) size 800x100
-  RenderSVGRoot {svg} at (0,50) size 800x100
-layer at (0,304) size 800x100
-  RenderSVGRoot {svg} at (0,50) size 800x100
 layer at (20,50) size 717x58
   RenderBlock (positioned) {div} at (20,50) size 717x58
     RenderInline {span} at (0,0) size 95x56 [textStrokeWidth=1.00]
@@ -35,6 +31,8 @@ layer at (20,50) size 717x58
     RenderText {#text} at (505,1) size 212x56
       text run at (505,1) width 15: " "
       text run at (519,1) width 198: "shadows"
+layer at (0,100) size 800x100
+  RenderSVGRoot {svg} at (0,50) size 800x100
 layer at (0,100) size 800x100
   RenderSVGViewportContainer at (0,0) size 800x100
 layer at (20,121) size 717x56
@@ -73,6 +71,8 @@ layer at (20,254) size 717x58
     RenderText {#text} at (505,1) size 212x56
       text run at (505,1) width 15: " "
       text run at (519,1) width 198: "shadows"
+layer at (0,304) size 800x100
+  RenderSVGRoot {svg} at (0,50) size 800x100
 layer at (0,304) size 800x100
   RenderSVGViewportContainer at (0,0) size 800x100
 layer at (20,325) size 717x56

LayoutTests/platform/mac-monterey-wk2-lbse-text/svg/custom/image-parent-translation-expected.txt

@@ -22,14 +22,14 @@ layer at (0,0) size 800x219
         RenderText {#text} at (0,0) size 0x0
 layer at (8,132) size 75x75
   RenderSVGRoot {svg} at (0,0) size 75x75
-layer at (87,132) size 75x75
-  RenderSVGRoot {svg} at (79,0) size 75x75
 layer at (8,132) size 75x75
   RenderSVGViewportContainer at (0,0) size 75x75
 layer at (8,132) size 75x75
   RenderSVGImage {image} at (0,0) size 75x75
 layer at (8,132) size 75x75
   RenderSVGRect {rect} at (0,0) size 75x75 [stroke={[type=SOLID] [color=#FF0000] [stroke width=6.00]}] [x=0.00] [y=0.00] [width=75.00] [height=75.00]
+layer at (87,132) size 75x75
+  RenderSVGRoot {svg} at (79,0) size 75x75
 layer at (87,132) size 75x75
   RenderSVGViewportContainer at (0,0) size 75x75
 layer at (87,132) size 75x75

LayoutTests/platform/mac-monterey-wk2-lbse-text/svg/custom/second-inline-text-expected.txt

@@ -12,8 +12,6 @@ layer at (0,0) size 800x162
         RenderText {#text} at (0,0) size 0x0
 layer at (8,50) size 100x100
   RenderSVGRoot {svg} at (0,0) size 100x100
-layer at (112,50) size 100x100
-  RenderSVGRoot {svg} at (104,0) size 100x100
 layer at (8,50) size 100x100
   RenderSVGViewportContainer at (0,0) size 100x100
 layer at (36,69) size 45x63
@@ -22,6 +20,8 @@ layer at (18,86) size 38x18
   RenderSVGText {text} at (10,36) size 39x18 contains 1 chunk(s)
     RenderSVGInlineText {#text} at (0,0) size 39x18
       chunk 1 text run 1 at (10.00,50.00) startOffset 0 endOffset 4 width 38.25: "PASS"
+layer at (112,50) size 100x100
+  RenderSVGRoot {svg} at (104,0) size 100x100
 layer at (112,50) size 100x100
   RenderSVGViewportContainer at (0,0) size 100x100
 layer at (140,69) size 45x63

Source/WebCore/style/StyleAdjuster.cpp

@@ -709,7 +709,8 @@ void Adjuster::adjustSVGElementStyle(RenderStyle& style, const SVGElement& svgEl
         ASSERT(!style.clipPath());
         ASSERT(!style.hasFilter());
 
-        if (svgElement.hasTagName(SVGNames::foreignObjectTag)
+        if (svgElement.isOutermostSVGSVGElement()
+            || svgElement.hasTagName(SVGNames::foreignObjectTag)
             || svgElement.hasTagName(SVGNames::imageTag)
             || svgElement.hasTagName(SVGNames::markerTag)
             || svgElement.hasTagName(SVGNames::maskTag)