pythongh-100428: Make int documentation more accurate

- Remove first link to lexical definition of integer literal, since it
  doesn't apply (differs in handling of leading zeros, base needs to be
  explicitly specified, unicode digits are allowed)
- Better describe handling of leading zeros and unicode digits
- Base 0 does not work exactly as like a code literal, since it allows
  Unicode digits. Link code literal to lexical definition of integer
  literal.

Doc/library/functions.rst

@@ -890,17 +890,20 @@ are always available. They are listed here in alphabetical order.
  For floating point numbers, this truncates towards zero.
 
  If *x* is not a number or if *base* is given, then *x* must be a string,
- :class:`bytes`, or :class:`bytearray` instance representing an :ref:`integer
- literal <integers>` in radix *base*. Optionally, the literal can be
- preceded by ``+`` or ``-`` (with no space in between) and surrounded by
- whitespace. A base-n literal consists of the digits 0 to n-1, with ``a``
+ :class:`bytes`, or :class:`bytearray` instance representing an integer
+ literal in radix *base*. Optionally, the literal can be
+ preceded by ``+`` or ``-`` (with no space in between), have leading zeros,
+ or be surrounded by whitespace.
+
+ A base-n literal consists of Unicode digits representing 0 to n-1, with ``a``
  to ``z`` (or ``A`` to ``Z``) having
- values 10 to 35. The default *base* is 10. The allowed values are 0 and 2--36.
+ values 10 to 35. The default *base* is 10. The allowed bases are 0 and 2--36.
  Base-2, -8, and -16 literals can be optionally prefixed with ``0b``/``0B``,
  ``0o``/``0O``, or ``0x``/``0X``, as with integer literals in code. Base 0
- means to interpret exactly as a code literal, so that the actual base is 2,
- 8, 10, or 16, and so that ``int('010', 0)`` is not legal, while
- ``int('010')`` is, as well as ``int('010', 8)``.
+ means to interpret similar to a :ref:`code literal <integers>`, in that the
+ actual base is 2, 8, 10, or 16 as determined by the prefix. Base 0 also
+ disallows leading zeros: ``int('010', 0)`` is not legal, while ``int('010')``
+ and ``int('010', 8)`` are.
 
  The integer type is described in :ref:`typesnumeric`.