Modernize and test derived path JSON

Old code is now just used for `nix build` --- there is no CLI breaking
change.

Test the new format, too.

The new format is not currently used, but will be used going forward,
for example in the C API.

Progress on #13570

src/libstore-tests/data/derived-path/multi_built_built.json

@@ -0,0 +1,10 @@
+{
+  "drvPath": {
+    "drvPath": "g1w7hy3qg1w7hy3qg1w7hy3qg1w7hy3q-foo.drv",
+    "output": "bar"
+  },
+  "outputs": [
+    "baz",
+    "quux"
+  ]
+}

src/libstore-tests/data/derived-path/multi_built_built_wildcard.json

@@ -0,0 +1,9 @@
+{
+  "drvPath": {
+    "drvPath": "g1w7hy3qg1w7hy3qg1w7hy3qg1w7hy3q-foo.drv",
+    "output": "bar"
+  },
+  "outputs": [
+    "*"
+  ]
+}

src/libstore-tests/data/derived-path/multi_opaque.json

@@ -0,0 +1 @@
+"g1w7hy3qg1w7hy3qg1w7hy3qg1w7hy3q-foo.drv"

src/libstore-tests/data/derived-path/mutli_built.json

@@ -0,0 +1,7 @@
+{
+  "drvPath": "g1w7hy3qg1w7hy3qg1w7hy3qg1w7hy3q-foo.drv",
+  "outputs": [
+    "bar",
+    "baz"
+  ]
+}

src/libstore-tests/data/derived-path/single_built.json

@@ -0,0 +1,4 @@
+{
+  "drvPath": "g1w7hy3qg1w7hy3qg1w7hy3qg1w7hy3q-foo.drv",
+  "output": "bar"
+}

src/libstore-tests/data/derived-path/single_built_built.json

@@ -0,0 +1,7 @@
+{
+  "drvPath": {
+    "drvPath": "g1w7hy3qg1w7hy3qg1w7hy3qg1w7hy3q-foo.drv",
+    "output": "bar"
+  },
+  "output": "baz"
+}

src/libstore-tests/data/derived-path/single_opaque.json

@@ -0,0 +1 @@
+"g1w7hy3qg1w7hy3qg1w7hy3qg1w7hy3q-foo.drv"