Fix sourcemap prefix path substitution on windows (#23936)

Normalize prefixes instead of expecting windows users to do it. 

See
#23741 (comment)

The tests now pass on windows.

Author: lvlte

test/test_other.py

@@ -10476,7 +10476,6 @@ def test_wasm_sourcemap(self, sources, prefix, load_prefix, basepath):
     'sources': ([], 1)
   })
   @crossplatform
-  @no_windows('https://github.com/emscripten-core/emscripten/pull/23741#issuecomment-2725574867')
   def test_emcc_sourcemap_options(self, prefixes, sources):
     wasm_sourcemap = importlib.import_module('tools.wasm-sourcemap')
     cwd = os.getcwd()

tools/wasm-sourcemap.py

@@ -55,10 +55,10 @@ def __init__(self, args, base_path=None, preserve_deterministic_prefix=True):
     for p in args:
       if '=' in p:
         prefix, replacement = p.split('=')
-        prefixes.append({'prefix': prefix, 'replacement': replacement})
+        prefixes.append({'prefix': utils.normalize_path(prefix), 'replacement': replacement})
       else:
-        prefixes.append({'prefix': p, 'replacement': ''})
-    self.base_path = base_path
+        prefixes.append({'prefix': utils.normalize_path(p), 'replacement': ''})
+    self.base_path = utils.normalize_path(base_path) if base_path is not None else None
     self.preserve_deterministic_prefix = preserve_deterministic_prefix
     self.prefixes = prefixes
     self.cache = {}