Merge bitcoin/bitcoin#22528: refactor: move GetTransaction to node/transaction.cpp

f685a13bef0418663015ea6d8f448f075510c0ec doc: GetTransaction()/getrawtransaction follow-ups to #22383 (John Newbery)
abc57e1f0882a1a2bb20474648419979af6e383d refactor: move `GetTransaction(...)` to node/transaction.cpp (Sebastian Falbesoner)

Pull request description:

  ~This PR is based on #22383, which should be reviewed first~ (merged by now).

  In [yesterday's PR review club session to PR 22383](https://bitcoincore.reviews/22383), the idea of moving the function `GetTransaction(...)` from src/validation.cpp to src/node/transaction.cpp came up. With this, the circular dependency "index/txindex -> validation -> index/txindex" is removed (see change in `lint-circular-dependencies.sh`). Thanks to jnewbery for suggesting and to sipa for providing historical background.

  Relevant IRC log:
  ```
  17:52 <jnewbery> Was anyone surprised that GetTransaction() is in validation.cpp? It seems to me that node/transaction.cpp would be a more appropriate place for it.
  17:53 <raj_> jnewbery, +1
  17:53 <stickies-v> agreed!
  17:54 <glozow> jnewbery ya
  17:54 <jnewbery> seems weird that validation would call into txindex. I wonder if we remove this function, then validation would no longer need to #include txindex
  17:54 <sipa> GetTransaction predates node/transaction.cpp, and even the generic index framework itself :)
  17:55 <sipa> (before 0.8, validation itself used the txindex)
  17:55 <jnewbery> (and GetTransaction() seems like a natural sibling to BroadcastTransaction(), which is already in node/transaction.cpp)
  17:55 <jnewbery> sipa: right, this is not meant as a criticism of course. Just wondering if we can organize things a bit more rationally now that we have better separation between things.
  17:55 <sipa> jnewbery: sure, just providing background
  17:56 <sipa> seems very reasonable to move it elsewhere now
  ```

  The commit should be trivial to review with `--color-moved`.

ACKs for top commit:
  jnewbery:
    Code review ACK f685a13bef0418663015ea6d8f448f075510c0ec
  rajarshimaitra:
    tACK https://github.com/bitcoin/bitcoin/pull/22528/commits/f685a13bef0418663015ea6d8f448f075510c0ec
  mjdietzx:
    crACK f685a13bef0418663015ea6d8f448f075510c0ec
  LarryRuane:
    Code review, test ACK f685a13bef0418663015ea6d8f448f075510c0ec

Tree-SHA512: 0e844a6ecb1be04c638b55bc4478c2949549a4fcae01c984eee078de74d176fb19d508fc09360a62ad130677bfa7daf703b67870800e55942838d7313246248c

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