[jsinterp] Overhaul JSInterp to handle new YT players 4c3f79c5, 324f67b9 (#31170)

* back-port from yt-dlp 8f53dc44a0cc1c2d98c35740b9293462c080f5d0, thanks pukkandan
* also support void, improve <</>> precedence, improve expressions in comma-list
* add more tests

youtube_dl/compat.py

@@ -2985,7 +2985,6 @@ except ImportError:
     except ImportError:
         compat_filter = filter
 
-
 try:
     from future_builtins import zip as compat_zip
 except ImportError:  # not 2.6+ or is 3.x
@@ -2995,6 +2994,57 @@ except ImportError:  # not 2.6+ or is 3.x
         compat_zip = zip
 
 
+# method renamed between Py2/3
+try:
+    from itertools import zip_longest as compat_itertools_zip_longest
+except ImportError:
+    from itertools import izip_longest as compat_itertools_zip_longest
+
+
+# new class in collections
+try:
+    from collections import ChainMap as compat_collections_chain_map
+except ImportError:
+    # Py < 3.3
+    class compat_collections_chain_map(compat_collections_abc.MutableMapping):
+
+        maps = [{}]
+
+        def __init__(self, *maps):
+            self.maps = list(maps) or [{}]
+
+        def __getitem__(self, k):
+            for m in self.maps:
+                if k in m:
+                    return m[k]
+            raise KeyError(k)
+
+        def __setitem__(self, k, v):
+            self.maps[0].__setitem__(k, v)
+            return
+
+        def __delitem__(self, k):
+            if k in self.maps[0]:
+                del self.maps[0][k]
+                return
+            raise KeyError(k)
+
+        def __iter__(self):
+            return itertools.chain(*reversed(self.maps))
+
+        def __len__(self):
+            return len(iter(self))
+
+        def new_child(self, m=None, **kwargs):
+            m = m or {}
+            m.update(kwargs)
+            return compat_collections_chain_map(m, *self.maps)
+
+        @property
+        def parents(self):
+            return compat_collections_chain_map(*(self.maps[1:]))
+
+
 if sys.version_info < (3, 3):
     def compat_b64decode(s, *args, **kwargs):
         if isinstance(s, compat_str):
@@ -3031,6 +3081,7 @@ __all__ = [
     'compat_basestring',
     'compat_chr',
     'compat_collections_abc',
+    'compat_collections_chain_map',
     'compat_cookiejar',
     'compat_cookiejar_Cookie',
     'compat_cookies',
@@ -3051,6 +3102,7 @@ __all__ = [
     'compat_input',
     'compat_integer_types',
     'compat_itertools_count',
+    'compat_itertools_zip_longest',
     'compat_kwargs',
     'compat_map',
     'compat_numeric_types',