Meta issue: improve documentation for implementation of the PEP 3118 in Python

Documentation

Recent d.p.o discussion thread and SC decision reveal some problems with current docs. Affected parts are the memoryview and struct/array/ctypes modules. I'll list issues in a random order with a hope that people will extend/correct this list:

• The struct module docs has Format Characters section. Though, some type codes now have more than one character. We should rename this section and use some different term. Format Codes? // https://github.com/python/cpython/pull/149483
• array docs says: The type is specified at object creation time by using a type code, which is a single character. // https://github.com/python/cpython/pull/149483
• memoryview docs are too vague in their references to the struct module:
  • "format" described as being "in struct module style"
  • it might be not clear that means "single element native format" (C type with native byte size, native endianness, and native alignment)
• ctypes has no documentation for the buffer protocol support at all; though, it's probably most advanced across of the stdlib, see Lib/test/test_ctypes/test_pep3118.py.
• ctypes._SimpleCData._type_ docs says "Class attribute that contains an internal type code, as a single-character string. See Fundamental data types for a summary." // https://github.com/python/cpython/pull/149483

Linked PRs

• gh-149483

先从 memoryview、struct、array 和 ctypes 的文档部分开始，然后阅读链接的讨论以及 SC 关于 PEP 3118 预期术语的决定。使用 Lib/test/test_ctypes/test_pep3118.py 了解现有的 ctypes buffer protocol 行为。完成的标准是：memoryview 格式引用准确，并且 ctypes 缓冲区支持已有文档说明。