Issue #18582: fix memory leak in pbkdf2 code
Issue #19512: sys_displayhook() now uses an identifier for "builtins"
dictionary key and only decodes "\n" string once to write a newline.

So "builtins" and "\n" are only decoded once from UTF-8, at the first call.
Issue #19512: _print_total_refs() now uses an identifier to get "showrefcount"
key from sys._xoptions
Issue #19512: Add PyRun_InteractiveOneObject() function

Only decode the filename once. PyRun_InteractiveOneObject() uses an identifier
for "<string>" string, so the byte string is only decoded once.
Issue #19512: Py_ReprEnter() and Py_ReprLeave() now use an identifier for the
"Py_Repr" dictionary key
Issue #19512: Add a new _PyDict_DelItemId() function, similar to
PyDict_DelItemString() but using an identifier for the key
Issue #19512: type_abstractmethods() and type_set_abstractmethods() now use an
identifier for the "__abstractmethods__" string
Issue #19512: eval() and exec() now use an identifier for "__builtins__" string
Issue #19512: Add _PySys_GetObjectId() and _PySys_SetObjectId() functions
Issue #19512: PRINT_EXPR bytecode now uses an identifier to get sys.displayhook
to only create the "displayhook" string once
Issue #19512: pickle now uses an identifier to only create the Unicode string
"modules" once
Issue #19512: add some common identifiers to only create common strings once,
instead of creating temporary Unicode string objects

Add also more identifiers in pythonrun.c to avoid temporary Unicode string
objets for the interactive interpreter.
Issue #19512: __build_class() builtin now uses an identifier for the "metaclass" string
Issue #19512: fileio_init() reuses PyId_name identifier instead of "name"
literal string
Issue #19512: _count_elements() of _collections reuses PyId_get identifier
instead of literal "get" string
Issue #19512: builtin print() function uses an identifier instead of literal
string "flush" to call the flush method
print_exception(): don't encode the module name to UTF-8

Replace _PyUnicode_AsString()+strcmp() with PyUnicode_CompareWithASCIIString().
Issue #19512: add _PyUnicode_CompareWithId() function

_PyUnicode_CompareWithId() is faster than PyUnicode_CompareWithASCIIString()
when both strings are equal and interned.

Add also _PyId_builtins identifier for "builtins" common string.
Issue #19512: Use the new _PyId_builtins identifier
remove an outdated comment

The comment is meaningless since changeset 4e985a96a612.