Move test running code from test.support to libregrtest

[serhiy-storchaka]

test.support.run_unittest() was used to run unit tests, but now all tests are collected using standard unittest mechanism. Currently it is only used in libregrtest, and its code can be moved there.

test.support.run_doctest() was used to run doctests, but now they are integrated in unit tests using DocTestSuite and DocFileSuite. It is no longer used, and can be removed.

Linked PRs

• gh-111165: Move test running code from test.support to libregrtest #111166
• [3.12] gh-111165: Move test running code from test.support to libregrtest (GH-111166) #111316
• [3.11] [3.12] gh-111165: Move test running code from test.support to libregrtest (GH-111166) (GH-111316) #111318
• gh-111165: Add missed "support." prefix for "verbose" #111327
• [3.12] gh-111165: Add missed "support." prefix for "verbose" (GH-111327) #111328
• [3.11] gh-111165: Add missed "support." prefix for "verbose" (GH-111327) #111329
• gh-111165: Remove documentation for moved functions #111467
• [3.12] gh-111165: Remove documentation for moved functions (GH-111467) #111471
• [3.11] gh-111165: Remove documentation for moved functions (GH-111467). #111472

[serhiy-storchaka]

cc @vstinner