py/objtype: Add support for PEP487 __set_name__.

This commit adds support for the `__set_name__` data model method specified
by PEP487 - Simpler customisation of class creation.

This includes support for methods that mutate the owner class, and avoids
the naive modify-while-iterating hazard possible in a naive implementation
like micropython/micropython#15503.

Note that based on the benchmarks in micropython/micropython#16825, this is
also as fast or faster than the naive implementation, thanks to clever data
layout in `setname_list_t`, and the way this allows the capture step to run
during an existing loop through the class dict.

Other rejected approaches for dealing with the hazard include:

- python/cpython#72983
During the implementation of this feature for MicroPython, it was
discovered that some versions of CPython also have this naive hazard.
CPython resolved this bug in BPO-28797 and now makes a complete flat copy
of the class's dict to iterate.  This design decision doesn't make much
sense for a microcontroller though, even if it's perfectly reasonable in
the desktop world where memcpy might actually be cheaper than a
hard-to-branch-predict conditional; and it's also motivated in their case
by error-tracing considerations.

- micropython/micropython#16816
This is an equivalent implementation to CPython's approach that places this
copy directly on the stack; however it is both slower and has larger code
size than the approach taken here.

- micropython/micropython#15503
The simplest implementation is to just not worry about it and let the user
face the consequences if they mutate the owner class.  That's not a very
friendly behavior, though, and it's not actually much more performant than
this implementation on either time or code size.

- micropython/micropython#17693
Another alternative is to do the same as #15503 but leverage MicroPython's
existing `is_fixed` field in its dict type to convert attempted mutations
of the owner dict into `AttributeError`s.  This is safer than just leaving
the open hazard, but there's still important use-cases for owner-mutating
descriptors, and the performance gain is small enough that it isn't worth
missing support for those cases.

- combined micropython/micropython#17693 with this
Another version of this feature used a new feature define,
`MICROPY_PY_METACLASSES_LITE`, to control whether this algorithm or the
naive version is used.  This was rejected in favor of simplicity, based on
the very limited performance margin the naive version has (which in some
cases even goes _against_ it).

Signed-off-by: Anson Mansfield <amansfield@mantaro.com>

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