Various minor cleanups to WASM code generation

* Add newline function to code_builder
* Remove type aliases which made jump to definition less ergonomic
* Add types to constants

PiperOrigin-RevId: 827863199
Change-Id: Ib4390d398926466ecce491a3d0ebe308ed5e0cbe

wasm/codegen/helpers/code_builder.py

@@ -36,6 +36,10 @@ class CodeBuilder:
     else:
       self._lines.append("")
 
+  def newline(self) -> None:
+    """Adds a newline."""
+    self.line("")
+
   def to_string(self) -> str:
     """Returns the complete code string."""
     return "\n".join(self._lines)