Add PartiQL Playground proof of concept (PoC) (#127)

* Add PartiQL Playground proof of concept (PoC)

This change adds the PartiQL Playground proof of concept and includes:
- Enable JSON serialization on PartiQL AST and Parser result.

- Adds the new `partiql-playground` package.
- Add the required Front-end work for the proof-of-concept:
  - Putting a layout in place.
  - Use already available ace-editor PartiQL mode.
  - Add collapsable JSON and Graph representation.
  - Adds the `README` guide.

* Apply comment suggestions
 * Co-authored-by: Alan Cai <caialan@amazon.com>

.gitmodules

@@ -1,3 +1,6 @@
 [submodule "partiql-conformance-tests/partiql-tests"]
 	path = partiql-conformance-tests/partiql-tests
 	url = https://github.com/partiql/partiql-tests.git
+[submodule "partiql-playground/ace-builds"]
+	path = partiql-playground/ace-builds
+	url = https://github.com/ajaxorg/ace-builds.git

Cargo.toml

@@ -9,5 +9,6 @@ members = [
   "partiql-eval",
   "partiql-irgen",
   "partiql-parser",
+  "partiql-playground",
   "partiql-rewriter",
 ]

partiql-ast/Cargo.toml

@@ -25,6 +25,7 @@ partiql-source-map = { path = "../partiql-source-map" }
 
 derive_builder = "~0.11.1"
 rust_decimal = "~1.22.0"
+serde = { version = "~1.0.137", features = ["derive"] }
 
 [dev-dependencies]