Use SupportsIndex where applicable in builtins.pyi

[BvB93]

Follow up on #5694.

This PR replaces (where applicable) all remaining cases of int-based annotations with SupportsIndex.

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

werkzeug (https://github.com/pallets/werkzeug.git)
+ src/werkzeug/datastructures.pyi:41: error: Argument 1 of "__imul__" is incompatible with supertype "list"; supertype defines the argument type as "SupportsIndex"
+ src/werkzeug/datastructures.pyi:41: note: This violates the Liskov substitution principle
+ src/werkzeug/datastructures.pyi:41: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#incompatible-overrides
+ src/werkzeug/datastructures.pyi:41: error: Argument 1 of "__imul__" is incompatible with "__mul__" of supertype "list"; supertype defines the argument type as "SupportsIndex"
+ src/werkzeug/datastructures.pyi:41: error: Signatures of "__imul__" and "__mul__" are incompatible
+ src/werkzeug/datastructures.pyi:48: error: Argument 1 of "insert" is incompatible with supertype "list"; supertype defines the argument type as "SupportsIndex"
+ src/werkzeug/datastructures.pyi:48: note: This violates the Liskov substitution principle
+ src/werkzeug/datastructures.pyi:48: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#incompatible-overrides
+ src/werkzeug/datastructures.pyi:49: error: Argument 1 of "pop" is incompatible with supertype "list"; supertype defines the argument type as "SupportsIndex"
+ src/werkzeug/datastructures.pyi:49: note: This violates the Liskov substitution principle
+ src/werkzeug/datastructures.pyi:49: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#incompatible-overrides
- tests/test_wrappers.py:370: error: Function is missing a return type annotation
- tests/test_wrappers.py:388: error: Function is missing a return type annotation
- tests/test_wrappers.py:388: note: Use "-> None" if function does not return a value
- tests/test_wrappers.py:423: error: Function is missing a return type annotation
- tests/test_wrappers.py:423: note: Use "-> None" if function does not return a value
- tests/test_wrappers.py:648: error: Function is missing a type annotation
- tests/test_wrappers.py:682: error: Function is missing a return type annotation
- tests/test_wrappers.py:682: note: Use "-> None" if function does not return a value
- tests/test_wrappers.py:691: error: Function is missing a return type annotation
- tests/test_wrappers.py:693: error: Function is missing a type annotation
- tests/test_wrappers.py:696: error: Function is missing a type annotation
- tests/test_wrappers.py:699: error: Function is missing a type annotation
- tests/test_wrappers.py:710: error: Function is missing a return type annotation
- tests/test_wrappers.py:710: note: (Skipping most remaining errors due to unresolved imports or missing stubs; fix these first)
+ tests/test_wrappers.py:370: note: (Skipping most remaining errors due to unresolved imports or missing stubs; fix these first)