Add support for vfs assets in mj_compile function to MuJoCo WASM.

Regarding mj_compile VFS argument:
I was encountering a memory error when using `std::optional<MjVFS>` with `mj_compile` (because vfs should be an optional argument of the function). This is likely because `MjVFS` doesn't have copy/move constructors, which are required for types used with `std::optional`, causing issues with memory management when std::optional copies the MjVFS object.
To solve this and to make vfs an optional argument to `mj_compile`, I replaced `mj_compile_wrapper` with two overloaded functions. This avoids using `std::optional<MjVFS>` and resolves the memory issue, while still allowing mj_compile to be called with or without the vfs argument from JavaScript.

But what if we instead add those copy/move constructors so it works with `std::optional`?:
While making `MjVFS` copyable or movable would theoretically allow it to work with std::optional, it's not a feasible approach in this case.
The MjVFS struct manages file data in memory, allocating buffers when files are added and freeing them when `mj_deleteVFS` is called in its destructor. A copy would require a deep copy of the entire virtual filesystem, but MuJoCo does not provide a public API function (like a  "mj_copyVFS") to do this. Implementing a deep copy manually would be complex and fragile. A shallow copy would result in multiple MjVFS objects pointing to the same memory, leading to double-free errors when their destructors run.
Given these constraints, MjVFS cannot safely be made copyable. The approach of providing two overloaded C++ functions is better.

PiperOrigin-RevId: 855740541
Change-Id: Ia08b6db8868ad245f07145db3fb0322cb9f737cb

wasm/codegen/generators/constants.py

@@ -64,12 +64,16 @@ _SKIPPED_PLUGIN_FUNCTIONS: tuple[str, ...] = (
 # Functions that are bound as class methods
 _SKIPPED_CLASS_METHODS: tuple[str, ...] = (
     # go/keep-sorted start
+    "mj_addBufferVFS",
     "mj_copyData",
     "mj_copyModel",
     "mj_copySpec",
+    "mj_defaultVFS",
     "mj_deleteData",
+    "mj_deleteFileVFS",
     "mj_deleteModel",
     "mj_deleteSpec",
+    "mj_deleteVFS",
     "mj_loadXML",
     "mj_makeData",
     "mj_makeSpec",
@@ -113,11 +117,9 @@ _SKIPPED_ASSET_CACHE_FUNCTIONS: tuple[str, ...] = (
 # Omitted Virtual Filesystem (VFS) functions
 _SKIPPED_VFS_FUNCTIONS: tuple[str, ...] = (
     # go/keep-sorted start
-    "mj_addBufferVFS",
     "mj_addFileVFS",
-    "mj_defaultVFS",
-    "mj_deleteFileVFS",
-    "mj_deleteVFS",
+    "mj_mountVFS",
+    "mj_unmountVFS",
     # go/keep-sorted end
 )
 
@@ -187,17 +189,6 @@ _SKIPPED_UTILITY_FUNCTIONS: tuple[str, ...] = (
     # go/keep-sorted end
 )
 
-# Functions that require special wrappers.
-# These functions are not bound automatically but are written by hand instead.
-MANUAL_WRAPPER_FUNCTIONS: tuple[str, ...] = (
-    # go/keep-sorted start
-    "mj_compile",
-    "mj_saveLastXML",
-    "mj_setLengthRange",
-    "mju_error",
-    # go/keep-sorted end
-)
-
 # List of functions that should be skipped during the code generation process.
 SKIPPED_FUNCTIONS: tuple[str, ...] = (
     _SKIPPED_CLASS_METHODS
@@ -232,12 +223,24 @@ SKIPPED_STRUCTS: tuple[str, ...] = (
     # go/keep-sorted end
 )
 
+# Functions that require special wrappers.
+# These functions are not bound automatically but are written by hand instead.
+MANUAL_WRAPPER_FUNCTIONS: tuple[str, ...] = (
+    # go/keep-sorted start
+    "mj_compile",
+    "mj_saveLastXML",
+    "mj_setLengthRange",
+    "mju_error",
+    # go/keep-sorted end
+)
+
 # Structs for which header generation is done manually.
 # mjvScene is included here because buffer sizes need to be calculated based on
 # introspect doc strings, which was considered a brittle unreliable solution in
 # the past.
 MANUAL_STRUCTS_HEADERS: tuple[str, ...] = (
     "mjvScene",
+    "mjVFS",
 )
 # Structs for which source code generation is done manually.
 MANUAL_STRUCTS_SOURCES: tuple[str, ...] = (

wasm/codegen/generators/functions.py

@@ -272,8 +272,9 @@ def generate(
 
   function_bindings = []
   for func in sorted(functions, key=lambda f: f.name):
-    w = common.wrapped_function_name(func)
-    function_bindings.append(f'function("{func.name}", &{w});')
+    if func.name not in constants.MANUAL_WRAPPER_FUNCTIONS:
+      w = common.wrapped_function_name(func)
+      function_bindings.append(f'function("{func.name}", &{w});')
   bindings_content = "\n".join(function_bindings)
 
   return [