, bitcoin#24021, bitcoin#24543, bitcoin#26844, bitcoin#25325, bitcoin#28165, partial bitcoin#20524, bitcoin#26036, bitcoin#27981 (networking backports: part 7)

76a458e fmt: apply formatting suggestions from `clang-format-diff.py` (Kittywhiskers Van Gogh)
63962ec merge bitcoin#28165: transport abstraction (Kittywhiskers Van Gogh)
c6b9186 merge bitcoin#25325: Add pool based memory resource (Kittywhiskers Van Gogh)
8c986d6 partial bitcoin#27981: Fix potential network stalling bug (Kittywhiskers Van Gogh)
13f6dc1 merge bitcoin#26844: Pass MSG_MORE flag when sending non-final network messages (Kittywhiskers Van Gogh)
caaa0fd net: use `std::deque` for `vSendMsg` instead of `std::list` (Kittywhiskers Van Gogh)
2ecba6b partial bitcoin#26036: add NetEventsInterface::g_msgproc_mutex (Kittywhiskers Van Gogh)
f6c9439 merge bitcoin#24543: Move remaining globals into PeerManagerImpl (Kittywhiskers Van Gogh)
dbe41ea refactor: move object request logic to `PeerManagerImpl` (Kittywhiskers Van Gogh)
112c4e0 merge bitcoin#24021: Rename and move PoissonNextSend functions (Kittywhiskers Van Gogh)
6d690ed merge bitcoin#23970: Remove pointless and confusing shift in RelayAddress (Kittywhiskers Van Gogh)
87205f2 merge bitcoin#21327: ignore transactions while in IBD (Kittywhiskers Van Gogh)
51ad8e4 merge bitcoin#21148: Split orphan handling from net_processing into txorphanage (Kittywhiskers Van Gogh)
cbff29a partial bitcoin#20524: Move MIN_VERSION_SUPPORTED to p2p.py (Kittywhiskers Van Gogh)

Pull request description:

  ## Additional Information

  * Dependent on #6098

  * Dependent on #6233

  * `p2p_ibd_txrelay.py` was first introduced in [bitcoin#19423](bitcoin#19423) to test feefilter logic but on account of Dash not having feefilter capabilities, that backport was skipped over but on account of the tests introduced in [bitcoin#21327](bitcoin#21327) that test capabilities present in Dash, a minimal version of `p2p_ibd_txrelay.py` has been committed in.

  * `vSendMsg` is originally a `std::deque` and as an optimization, was changed to a `std::list` in 027a852 ([dash#3398](#3398)) but this renders us unable to backport [bitcoin#26844](bitcoin#26844) as it introduces build failures. The optimization has been reverted to make way for the backport.

    <details>

    <summary>Compile failure:</summary>

    ```
    net.cpp:959:20: error: invalid operands to binary expression ('iterator' (aka '_List_iterator<std::vector<unsigned char, std::allocator<unsigned char>>>') and 'int')
                if (it + 1 != node.vSendMsg.end()) {
                    ~~ ^ ~
    /usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/stl_bvector.h:303:3: note: candidate function not viable: no known conversion from 'iterator' (aka '_List_iterator<std::vector<unsigned char, std::allocator<unsigned char>>>') to 'ptrdiff_t' (aka 'long') for 1st argument
      operator+(ptrdiff_t __n, const _Bit_iterator& __x)
    [...]
    1 error generated.
    make[2]: *** [Makefile:11296: libbitcoin_server_a-net.o] Error 1
    make[2]: *** Waiting for unfinished jobs....
    make[2]: Leaving directory '/src/dash/src'
    make[1]: *** [Makefile:19171: all-recursive] Error 1
    make[1]: Leaving directory '/src/dash/src'
    make: *** [Makefile:799: all-recursive] Error 1
    ```

    </details>

  * The collection of `CNode` pointers in `CConnman::SocketHandlerConnected` has been changed to a `std::set` to allow for us to erase elements from `vReceivableNodes` if the node is _also_ in the set of sendable nodes and the send hasn't entirely succeeded to avoid a deadlock (i.e. backport [bitcoin#27981](bitcoin#27981))

  * When backporting [bitcoin#28165](bitcoin#28165), `denialofservice_tests` has been modified to still check with `vSendMsg` instead of `Transport::GetBytesToSend()` as changes in networking code to support LT-SEMs (level-triggered socket events mode) mean that the message doesn't get shifted from `vSendMsg` to `m_message_to_send`, as the test expects.
    * Specifically, the changes made for LT-SEM support result in the function responsible for making that shift (`Transport::SetMessageToSend()` through `CConnman::SocketSendData()`), not being called during the test runtime.

  * As checking `vSendMsg` (directly or through `nSendMsgSize`) isn't enough to determine if the queue is empty, we now also check with `to_send` from `Transport::GetBytesToSend()` to help us make that determination. This mirrors the change present in the upstream backport ([source](https://github.com/bitcoin/bitcoin/pull/28165/files#diff-00021eed586a482abdb09d6cdada1d90115abe988a91421851960e26658bed02R1324-R1327)).

  ## Breaking Changes

  * `bandwidth.message.*.bytesSent` will no longer include overhead and will now only report message size as specifics that let us calculate the overhead have been abstracted away.

  ## Checklist:

  - [x] I have performed a self-review of my own code
  - [x] I have commented my code, particularly in hard-to-understand areas **(note: N/A)**
  - [x] I have added or updated relevant unit/integration/functional/e2e tests
  - [x] I have made corresponding changes to the documentation **(note: N/A)**
  - [x] I have assigned this pull request to a milestone _(for repository code-owners and collaborators only)_

ACKs for top commit:
  PastaPastaPasta:
    utACK 76a458e

Tree-SHA512: 2e47c207c1f854cfbd5b28c07dd78e12765ddb919abcd7710325df5d253cd0ba4bc30aa21545d88519e8acfe65638a57db4ca66853aca82fc355542210f4b394