LibWeb/CSS: Implement the empty-cells property

This property sets whether table borders and backgrounds are painted
if a given table cell has no visible content.

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

@@ -11,6 +11,7 @@ All properties associated with getComputedStyle(document.body):
     "color-scheme",
     "cursor",
     "direction",
+    "empty-cells",
     "fill",
     "fill-opacity",
     "fill-rule",

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

@@ -327,6 +327,8 @@ All supported properties and their default values exposed from CSSStylePropertie
 'cy': '0px'
 'direction': 'ltr'
 'display': 'block'
+'emptyCells': 'show'
+'empty-cells': 'show'
 'fill': 'rgb(0, 0, 0)'
 'fillOpacity': '1'
 'fill-opacity': '1'

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

@@ -9,6 +9,7 @@ color: rgb(0, 0, 0)
 color-scheme: normal
 cursor: auto
 direction: ltr
+empty-cells: show
 fill: rgb(0, 0, 0)
 fill-opacity: 1
 fill-rule: nonzero
@@ -86,7 +87,7 @@ background-position-x: 0%
 background-position-y: 0%
 background-repeat: repeat
 background-size: auto auto
-block-size: 1320px
+block-size: 1335px
 border-block-end-color: rgb(0, 0, 0)
 border-block-end-style: none
 border-block-end-width: medium
@@ -151,7 +152,7 @@ grid-row-start: auto
 grid-template-areas: none
 grid-template-columns: none
 grid-template-rows: none
-height: 2295px
+height: 2310px
 inline-size: 784px
 inset-block-end: auto
 inset-block-start: auto