Merge #21575: refactor: Create blockstorage module

fadcd3f78e doc: Remove irrelevant link to GitHub (MarcoFalke)
fa121b628d blockstorage: [refactor] Use chainman reference where possible (MarcoFalke)
fa0c7d9ad2 move-only: Move *Disk functions to blockstorage (MarcoFalke)
fa91b2b2b3 move-only: Move AbortNode to shutdown (MarcoFalke)
fa413f07a1 move-only: Move ThreadImport to blockstorage (MarcoFalke)
faf843c07f refactor: Move load block thread into ChainstateManager (MarcoFalke)

Pull request description:

  This picks up the closed pull request #21030 and is the first step toward fixing #21220.

  The basic idea is to move all disk access into a separate module with benefits:
  * Breaking down the massive files init.cpp and validation.cpp into logical units
  * Creating a standalone-module to reduce the mental complexity
  * Pave the way to fix validation related circular dependencies
  * Pave the way to mock disk access for testing, especially where it is performance critical (like fuzzing)

ACKs for top commit:
  promag:
    Code review ACK fadcd3f78e, checked (almost) moved only changes. This is a nice tidy up change and doesn't change behavior. Easily reviewed commit by commit.
  jamesob:
    ACK fadcd3f78e ([`jamesob/ackr/21575.1.MarcoFalke.refactor_create_blocksto`](https://github.com/jamesob/bitcoin/tree/ackr/21575.1.MarcoFalke.refactor_create_blocksto))
  ryanofsky:
    Code review ACK fadcd3f78e. New organization makes sense, moves extraneous things outside of validation.cpp. PR is also easy to review with helpfully split up moveonly commits.

Tree-SHA512: 917996592b6d8f9998289d8cb2b1b78b23d1fdb3b07216c9caec1380df33baa09dc2c1e706da669d440b497e79c9c62a01ca20dc202df5ad974a75f3ef7a143b

src/index/base.cpp

@@ -4,12 +4,13 @@
 
 #include <chainparams.h>
 #include <index/base.h>
+#include <node/blockstorage.h>
 #include <node/ui_interface.h>
 #include <shutdown.h>
 #include <tinyformat.h>
 #include <util/system.h>
 #include <util/translation.h>
-#include <validation.h>
+#include <validation.h> // For g_chainman
 #include <warnings.h>
 
 constexpr char DB_BEST_BLOCK = 'B';

src/index/blockfilterindex.cpp

@@ -6,8 +6,8 @@
 
 #include <dbwrapper.h>
 #include <index/blockfilterindex.h>
+#include <node/blockstorage.h>
 #include <util/system.h>
-#include <validation.h>
 
 /* The index database stores three items for each block: the disk location of the encoded filter,
  * its dSHA256 hash, and the header. Those belonging to blocks on the active chain are indexed by