gh-95853: WASM: better version and asset handling in scripts (GH-96045)

- support EMSDK tot-upstream and git releases
- allow WASM assents for wasm64-emscripten and WASI. This makes single file distributions on WASI easier.
- decouple WASM assets from browser builds

Tools/wasm/wasm_assets.py

@@ -108,6 +108,14 @@ OMIT_MODULE_FILES = {
     "_zoneinfo": ["zoneinfo/"],
 }
 
+SYSCONFIG_NAMES = (
+    "_sysconfigdata__emscripten_wasm32-emscripten",
+    "_sysconfigdata__emscripten_wasm32-emscripten",
+    "_sysconfigdata__wasi_wasm32-wasi",
+    "_sysconfigdata__wasi_wasm64-wasi",
+)
+
+
 def get_builddir(args: argparse.Namespace) -> pathlib.Path:
     """Get builddir path from pybuilddir.txt
     """
@@ -120,7 +128,11 @@ def get_sysconfigdata(args: argparse.Namespace) -> pathlib.Path:
     """Get path to sysconfigdata relative to build root
     """
     data_name = sysconfig._get_sysconfigdata_name()
-    assert "emscripten_wasm32" in data_name
+    if not data_name.startswith(SYSCONFIG_NAMES):
+        raise ValueError(
+            f"Invalid sysconfig data name '{data_name}'.",
+            SYSCONFIG_NAMES
+        )
     filename = data_name + ".py"
     return args.builddir / filename