LibWeb: Parse the border-image-source property

Author: https://github.com/tcl3
Commit: 70c2621634
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/5253
Reviewed-by: https://github.com/AtkinsSJ ✅

Tests/LibWeb/Text/expected/css/CSSStyleDeclaration-has-indexed-property-getter.txt

@@ -105,6 +105,7 @@ All properties associated with getComputedStyle(document.body):
     "border-bottom-width",
     "border-end-end-radius",
     "border-end-start-radius",
+    "border-image-source",
     "border-inline-end-color",
     "border-inline-end-style",
     "border-inline-end-width",

Tests/LibWeb/Text/expected/css/CSSStyleProperties-all-supported-properties-and-default-values.txt

@@ -243,6 +243,8 @@ All supported properties and their default values exposed from CSSStylePropertie
 'border-end-end-radius': '0px'
 'borderEndStartRadius': '0px'
 'border-end-start-radius': '0px'
+'borderImageSource': 'none'
+'border-image-source': 'none'
 'borderInlineColor': 'rgb(0, 0, 0)'
 'border-inline-color': 'rgb(0, 0, 0)'
 'borderInlineEnd': '0px rgb(0, 0, 0)'

Tests/LibWeb/Text/expected/css/getComputedStyle-print-all.txt

@@ -103,6 +103,7 @@ border-bottom-style: none
 border-bottom-width: 0px
 border-end-end-radius: 0px
 border-end-start-radius: 0px
+border-image-source: none
 border-inline-end-color: rgb(0, 0, 0)
 border-inline-end-style: none
 border-inline-end-width: 0px
@@ -158,7 +159,7 @@ grid-row-start: auto
 grid-template-areas: none
 grid-template-columns: none
 grid-template-rows: none
-height: 2400px
+height: 2415px
 inline-size: 784px
 inset-block-end: auto
 inset-block-start: auto