Update and improve dev container: (#3977)

- Replace deprecated `crates` extension with `dependi`
- Add Playwright extension
- Simplify Dockerfile
- Add dependencies as specified in the Dioxus documentation
- Pre-install Playwright dependencies
- Adjust README.md

.devcontainer/devcontainer.json

@@ -30,7 +30,8 @@
             "extensions": [
                 "rust-lang.rust-analyzer",
                 "tamasfe.even-better-toml",
-                "serayuzgur.crates"
+                "fill-labs.dependi",
+                "ms-playwright.playwright"
             ]
         }
     }