Merge bitcoin/bitcoin#25067: validationinterface: make MainSignalsInstance() a class, drop unused forward declarations

ca1ac1f0e0fbabbe97666aca94024afb8104da06 scripted-diff: Rename MainSignalsInstance() class to MainSignalsImpl() (Jon Atack)
2aaec2352d14753e1f2d4bf4b11bbe6ad42edf5c refactor: remove unused forward declarations in validationinterface.h (Jon Atack)
23854f84024c292164ce49b3fefee2a9b4fe0831 refactor: make MainSignalsInstance() a class (Jon Atack)

Pull request description:

  Make MainSignalsInstance a class, rename it to MainSignalsImpl, use Doxygen documentation for it, and remove no longer used forward declarations in src/validationinterface.h.

  ----

  MainSignalsInstance was created in 3a19fed9db5 and originally was a collection of boost::signals methods moved to validationinterface.cpp, in order to no longer need to include boost/signals in validationinterface.h.

  MainSignalsInstance then evolved in d6815a23131 to become class-like:

  - [C.8: Use class rather than struct if any member is non-public](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Rc-class)

   - [C.2: Use class if the class has an invariant; use struct if the data members can vary independently](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#c2-use-class-if-the-class-has-an-invariant-use-struct-if-the-data-members-can-vary-independently)

  - A class has the advantage of default private access, as opposed to public for a struct.

ACKs for top commit:
  furszy:
    Code ACK ca1ac1f
  promag:
    Code review ACK ca1ac1f0e0fbabbe97666aca94024afb8104da06.
  danielabrozzoni:
    Code review ACK ca1ac1f0e0fbabbe97666aca94024afb8104da06

Tree-SHA512: 25f85e2b582fe8c269e6cf384a4aa29350b97ea6477edf3c63591e4f68a97364f7fb2fc4ad2764f61ff86b27353e31d2f12eed7a23368a247e4cf271c7e133ea

1 files changed, 2 insertions, 4 deletions

diff --git a/src/validationinterface.h b/src/validationinterface.h
index ac62f8b467..a929a3d56b 100644
--- a/src/validationinterface.h
+++ b/src/validationinterface.h
@@ -17,9 +17,7 @@ class BlockValidationState;
 class CBlock;
 class CBlockIndex;
 struct CBlockLocator;
-class CConnman;
 class CValidationInterface;
-class uint256;
 class CScheduler;
 enum class MemPoolRemovalReason;
 
@@ -177,10 +175,10 @@ protected:
     friend class ValidationInterfaceTest;
 };
 
-struct MainSignalsInstance;
+class MainSignalsImpl;
 class CMainSignals {
 private:
-    std::unique_ptr<MainSignalsInstance> m_internals;
+    std::unique_ptr<MainSignalsImpl> m_internals;
 
     friend void ::RegisterSharedValidationInterface(std::shared_ptr<CValidationInterface>);
     friend void ::UnregisterValidationInterface(CValidationInterface*);