Move wasm file format code into a submodule

compiler/gen_wasm/src/wasm_module/mod.rs

@@ -0,0 +1,12 @@
+pub mod code_builder;
+pub mod opcodes;
+pub mod sections;
+pub mod serialize;
+
+pub use code_builder::{
+    Align, BlockType, CodeBuilder, LocalId, ValueType, VirtualMachineSymbolState,
+};
+pub use sections::{
+    Export, ExportType, Global, GlobalInitValue, GlobalType, LinkingSubSection, Signature, SymInfo,
+    WasmModule,
+};