Merge #13281: test: Move linters to test/lint, add readme

fa3c910bfe test: Move linters to test/lint, add readme (MarcoFalke)

Pull request description:

  This moves the checks and linters from `devtools` to a subfolder in `test`. (Motivated by my opinion that the dev tools are mostly for generating code and updating the repo whereas the linters are read-only checks.)

  Also, adds a readme to clarify that checks and linters are only meant to prevent bugs and user facing issues, not merely stylistic preference or inconsistencies. (This is motivated by the diversity in developers and work flows as well as existing code styles. It would be too disruptive to change all existing code to a single style or too burdensome to force all developers to adhere to a single style. Also note that our style guide is changing, so locking in at the wrong style "too early" would only waste resources.)

Tree-SHA512: 9b10e89f2aeaf0c8a9ae248aa891d74e0abf0569f8e5dfd266446efa8bfaf19f0ea0980abf0b0b22f0d8416ee90d7435d21a9f9285b66df43f370b7979173406

doc/developer-notes.md

@@ -647,7 +647,7 @@ Others are external projects without a tight relationship with our project.  Cha
 be sent upstream but bugfixes may also be prudent to PR against Bitcoin Core so that they can be integrated
 quickly.  Cosmetic changes should be purely taken upstream.
 
-There is a tool in contrib/devtools/git-subtree-check.sh to check a subtree directory for consistency with
+There is a tool in `test/lint/git-subtree-check.sh` to check a subtree directory for consistency with
 its upstream repository.
 
 Current subtrees include:
@@ -778,7 +778,7 @@ To create a scripted-diff:
     - `-BEGIN VERIFY SCRIPT-`
     - `-END VERIFY SCRIPT-`
 
-The scripted-diff is verified by the tool `contrib/devtools/commit-script-check.sh`
+The scripted-diff is verified by the tool `test/lint/commit-script-check.sh`
 
 Commit [`bb81e173`](https://github.com/bitcoin/bitcoin/commit/bb81e173) is an example of a scripted-diff.