wasm-builder: Make it easier to build a WASM binary (#4177)

Basically combines all the recommended calls into one
`build_using_defaults()` call or `init_with_defaults()` when there are
some custom changes required.

substrate/utils/wasm-builder/src/builder.rs

@@ -116,6 +116,39 @@ impl WasmBuilder {
 		WasmBuilderSelectProject { _ignore: () }
 	}
 
+	/// Build the WASM binary using the recommended default values.
+	///
+	/// This is the same as calling:
+	/// ```no_run
+	/// substrate_wasm_builder::WasmBuilder::new()
+	///    .with_current_project()
+	///    .import_memory()
+	///    .export_heap_base()
+	///    .build();
+	/// ```
+	pub fn build_using_defaults() {
+		WasmBuilder::new()
+			.with_current_project()
+			.import_memory()
+			.export_heap_base()
+			.build();
+	}
+
+	/// Init the wasm builder with the recommended default values.
+	///
+	/// In contrast to [`Self::build_using_defaults`] it does not build the WASM binary directly.
+	///
+	/// This is the same as calling:
+	/// ```no_run
+	/// substrate_wasm_builder::WasmBuilder::new()
+	///    .with_current_project()
+	///    .import_memory()
+	///    .export_heap_base();
+	/// ```
+	pub fn init_with_defaults() -> Self {
+		WasmBuilder::new().with_current_project().import_memory().export_heap_base()
+	}
+
 	/// Enable exporting `__heap_base` as global variable in the WASM binary.
 	///
 	/// This adds `-Clink-arg=--export=__heap_base` to `RUST_FLAGS`.

substrate/utils/wasm-builder/src/lib.rs

@@ -33,15 +33,9 @@
 //! use substrate_wasm_builder::WasmBuilder;
 //!
 //! fn main() {
-//!     WasmBuilder::new()
-//!         // Tell the builder to build the project (crate) this `build.rs` is part of.
-//!         .with_current_project()
-//!         // Make sure to export the `heap_base` global, this is required by Substrate
-//!         .export_heap_base()
-//!         // Build the Wasm file so that it imports the memory (need to be provided by at instantiation)
-//!         .import_memory()
-//!         // Build it.
-//!         .build()
+//!     // Builds the WASM binary using the recommended defaults.
+//!     // If you need more control, you can call `new` or `init_with_defaults`.
+//!     WasmBuilder::build_using_defaults();
 //! }
 //! ```
 //!