gh-59598: Strip leading whitespace in JSONDecoder.raw_decode

raw_decode currently ignores leading whitespace before JSON values,
raising JSONDecodeError on strings like '  {"key": "value"}'. This is
inconsistent with JSONDecoder.decode() which handles leading whitespace.

Add s = s.lstrip() at the start of raw_decode to strip leading
whitespace before decoding, matching the behavior of decode().

Author: mayank-dev-15

Lib/json/decoder.py

@@ -370,6 +370,8 @@ def raw_decode(self, s, idx=0):
         have extraneous data at the end.
 
         """
+        s = s.lstrip()
+
         try:
             obj, end = self.scan_once(s, idx)
         except StopIteration as err: