C API: Move limited C API tests from _testcapi to a new _testlimitedcapi extension

[vstinner]

Currently, the _testcapi C extension is partially built with the limited C API and partially with the non-limited C API. It can lead to some confusion: which API is being tested?

I proposed to create a new _testlimitedcapi extension which is only built with the limited C API. It can only access to the limited C API and so there is a lower risk to test the non-limited C API by mistake.

Linked PRs

• gh-116417: Add _testlimitedcapi C extension #116419
• [WIP] gh-116417: Move limited C API tests to _testlimitedcapi #116567
• gh-116417: Avoid PyFloat_AS_DOUBLE() in AC limited C API #116568
• gh-116417: Fix make check-c-globals for _testlimitedcapi #116570
• gh-116417: Move 4 limited C API test files to _testlimitedcapi #116571
• gh-116417: Argument Clinic: test generated Limited C API code for float args #116573
• gh-116417: Build _testinternalcapi with limited C API version 3.5 #116598
• gh-116417: Move limited C API list.c tests to _testlimitedcapi #116602
• gh-116417: Fix WASI build of _testlimitedcapi #116974
• gh-116417: Move limited C API abstract.c tests to _testlimitedcapi #116986
• gh-116417: Move limited C API unicode.c tests to _testlimitedcapi #116993
• gh-116417: Move limited C API long.c tests to _testlimitedcapi #117001
• gh-116417: Move limited C API dict.c tests to _testlimitedcapi #117006
• gh-116417: Move limited C API complex.c tests to _testlimitedcapi #117014