Block editor: Update WP_Theme_JSON_Resolver and improve its performance.

This commit includes the latest updates WP_Theme_JSON_Resolver class made in the block editor. Some of these updates improve the performance of the class.

Props Mamaduka, hellofromTonya, flixos90, jorgefilipecosta, oandregal, spacedmonkey, audrasjb, costdev, scruffian.
Closes #57545.

git-svn-id: https://develop.svn.wordpress.org/trunk@55231 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/data/themedir1/block-theme-child/styles/variation-b.json

@@ -0,0 +1,18 @@
+{
+	"version": 2,
+	"settings": {
+		"blocks": {
+			"core/post-title": {
+				"color": {
+					"palette": [
+						{
+							"slug": "dark",
+							"name": "Dark",
+							"color": "#010101"
+						}
+					]
+				}
+			}
+		}
+	}
+}

tests/phpunit/data/themedir1/block-theme/styles/variation-b.json

@@ -0,0 +1,18 @@
+{
+	"version": 2,
+	"settings": {
+		"blocks": {
+			"core/post-title": {
+				"color": {
+					"palette": [
+						{
+							"slug": "light",
+							"name": "Light",
+							"color": "#f1f1f1"
+						}
+					]
+				}
+			}
+		}
+	}
+}

tests/phpunit/data/themedir1/block-theme/theme.json

@@ -124,4 +124,4 @@
 			"area": "header"
 		}
 	]
-}
+}