Add YAML middleware that behaves like TOML and JSON (#1093)

src/snapshot_middleware/snapshots/librojo__snapshot_middleware__yaml__test__instance_from_vfs-2.snap

@@ -0,0 +1,27 @@
+---
+source: src/snapshot_middleware/yaml.rs
+expression: source
+---
+return {
+	string = "this is a string",
+	boolean = true,
+	integer = 1337,
+	float = 123456789.5,
+	["value-with-hypen"] = "it sure is",
+	sequence = {"wow", 8675309},
+	map = {
+		key = "value",
+		key2 = "value 2",
+		key3 = "value 3",
+	},
+	["nested-map"] = {{
+		key = "value",
+	}, {
+		key2 = "value 2",
+	}, {
+		key3 = "value 3",
+	}},
+	whatever_this_is = {"i imagine", "it's", "a", "sequence?"},
+	null1 = nil,
+	null2 = nil,
+}

src/snapshot_middleware/snapshots/librojo__snapshot_middleware__yaml__test__instance_from_vfs.snap

@@ -0,0 +1,21 @@
+---
+source: src/snapshot_middleware/yaml.rs
+expression: instance_snapshot
+---
+snapshot_id: "00000000000000000000000000000000"
+metadata:
+  ignore_unknown_instances: false
+  instigating_source:
+    Path: /foo.yaml
+  relevant_paths:
+    - /foo.yaml
+    - /foo.meta.json
+  context:
+    emit_legacy_scripts: true
+  specified_id: ~
+name: foo
+class_name: ModuleScript
+properties:
+  Source:
+    String: "return {\n\tstring = \"this is a string\",\n\tboolean = true,\n\tinteger = 1337,\n\tfloat = 123456789.5,\n\t[\"value-with-hypen\"] = \"it sure is\",\n\tsequence = {\"wow\", 8675309},\n\tmap = {\n\t\tkey = \"value\",\n\t\tkey2 = \"value 2\",\n\t\tkey3 = \"value 3\",\n\t},\n\t[\"nested-map\"] = {{\n\t\tkey = \"value\",\n\t}, {\n\t\tkey2 = \"value 2\",\n\t}, {\n\t\tkey3 = \"value 3\",\n\t}},\n\twhatever_this_is = {\"i imagine\", \"it's\", \"a\", \"sequence?\"},\n\tnull1 = nil,\n\tnull2 = nil,\n}"
+children: []