Problem:  Duplicate assignment in f_getregion().
Solution: Remove the duplicate assignment.  Also improve getregion()
          docs wording and fix an unrelated typo (zeertzjq)

closes: vim/vim#14154

https://github.com/vim/vim/commit/0df8f93bdaea77a1afb9f4eca94fe67ec73e6df2

Problem:  can only call getregion() for current buffer
Solution: Allow to retrieve selections from different buffers
          (Shougo Matsushita)

closes: vim/vim#14131

https://github.com/vim/vim/commit/84bf6e658da51126bdd2e50af1f40cabd149343f

Co-authored-by: Shougo Matsushita <Shougo.Matsu@gmail.com>

Problem:  has('pythonx') always returns 1.
Solution: Make it the same as has('python3').

Currently returns 0 on failure, but should return an empty list (or blob).

Regressed in the big blob port of '21 (#15211).

Problem:  getregion() can be improved (after v9.1.120)
Solution: change getregion() implementation to use pos as lists and
          one optional {opt} dictionary (Shougo Matsushita)

Note: The following is a breaking change!

Currently, the getregion() function (included as of patch v9.1.120) takes
3 arguments: the first 2 arguments are strings, describing a position,
arg3 is the type string.

However, that is slightly inflexible, there is no way to specify
additional arguments. So let's instead change the function signature to:

getregion(pos1, pos2 [, {Dict}]) where both pos1 and pos2 are lists.
This is slightly cleaner, and gives us the flexibility to specify
additional arguments as key/value pairs to the optional Dict arg.

Now it supports the "type" key to specify the selection type
(characterwise, blockwise or linewise) and now in addition one can also
define the selection type, independently of what the 'selection' option
actually is.

Technically, this is a breaking change, but since the getregion()
Vimscript function is still quite new, this should be fine.

closes: vim/vim#14090

https://github.com/vim/vim/commit/19b718828d8d5fab52d94c6cdba694641879ab38

Co-authored-by: Shougo Matsushita <Shougo.Matsu@gmail.com>

Then we can just load metadata in C as a single msgpack blob. Which also
can be used directly as binarly data, instead of first unpacking all the
functions and ui_events metadata to immediately pack it again, which was
a bit of a silly walk (and one extra usecase of `msgpack_rpc_from_object`
which will get yak shaved in the next PR)

Problem:  Naming a non-pointer variable "oap" is strange.
Solution: Rename it to "oa". Also prevent using freed memory in case of
          memory allocation failure. (zeertzjq)

closes: vim/vim#14075

https://github.com/vim/vim/commit/5e3674b42da10b7e7c72d1f20f9a15379af1b60a

Problem:  Internal error when passing mark in another buffer to
          getregion().
Solution: Don't allow marks in another buffer (zeertzjq)

closes: vim/vim#14076

Internal error when passing mark in another buffer to getregion()

https://github.com/vim/vim/commit/421b597470c118871c7081de00dd065e0e000b7e