Fix JSON parser handling for certain objects (#7162)

This PR also adds some comments and simplifies
the code. Primary handling is done to ensure
that we make sure to honor cached buffer.

Added unit tests as well

Fixes #7141

pkg/s3select/json/data/4.json

@@ -0,0 +1,26 @@
+{
+	"id": "0001",
+	"type": "donut",
+	"name": "Cake",
+	"ppu": 0.55,
+	"batters":
+		{
+			"batter":
+				[
+					{ "id": "1001", "type": "Regular" },
+					{ "id": "1002", "type": "Chocolate" },
+					{ "id": "1003", "type": "Blueberry" },
+					{ "id": "1004", "type": "Devil's Food" }
+				]
+		},
+	"topping":
+		[
+			{ "id": "5001", "type": "None" },
+			{ "id": "5002", "type": "Glazed" },
+			{ "id": "5005", "type": "Sugar" },
+			{ "id": "5007", "type": "Powdered Sugar" },
+			{ "id": "5006", "type": "Chocolate with Sprinkles" },
+			{ "id": "5003", "type": "Chocolate" },
+			{ "id": "5004", "type": "Maple" }
+		]
+}