[3.11] gh-103360: Add link in stdtypes.rst to escape sequences in lexical_analysis.rst (GH-103638)

[miss-islington]

(cherry picked from commit d29f57f)

Co-authored-by: Justin Williams [email protected]

• Issue: String escape sequences should be listed in the stdtypes page #103360

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📚 Documentation preview 📚: https://cpython-previews--114908.org.readthedocs.build/

[terryjreedy]

@serhiy-storchaka This 3.11 backport failed with
/home/runner/work/cpython/cpython/Doc/library/stdtypes.rst:1490: WARNING: undefined label: 'escape-sequences'
because the heading addition was not backported to 3.11. I will add it there and rurun the Docs test.

EDIT: I wish Close was separated from Comment button.