refactor: tidy up implementation of special tx manager (#5172)

## Issue being fixed or feature implemented
It is preparation work for #5026 (moved out a refactoring as a new pull
request)

## What was done?
 - tidy up header dependencies
 - move general code to proper headers


## How Has This Been Tested?
Run unit/functional tests

## Breaking Changes
No breaking changes

## Checklist:
- [x] I have performed a self-review of my own code
- [x] I have commented my code, particularly in hard-to-understand areas

**For repository code-owners and collaborators only**
- [x] I have assigned this pull request to a milestone

src/evo/providertx.h

@@ -13,21 +13,13 @@
 #include <key_io.h>
 #include <netaddress.h>
 #include <pubkey.h>
+#include <tinyformat.h>
 #include <univalue.h>
 
 class CBlockIndex;
 class CCoinsViewCache;
 class CValidationState;
 
-struct maybe_error{
-    bool did_err{false};
-    ValidationInvalidReason reason{ValidationInvalidReason::CONSENSUS};
-    std::string_view error_str;
-
-    constexpr maybe_error() = default;
-    constexpr maybe_error(ValidationInvalidReason reasonIn, std::string_view err): did_err(true), reason(reasonIn), error_str(err) {};
-};
-
 class CProRegTx
 {
 public:

src/evo/specialtx.h

@@ -5,14 +5,25 @@
 #ifndef BITCOIN_EVO_SPECIALTX_H
 #define BITCOIN_EVO_SPECIALTX_H
 
+#include <consensus/validation.h>
 #include <primitives/transaction.h>
 #include <serialize.h>
 #include <streams.h>
 #include <uint256.h>
 #include <version.h>
 
+#include <string_view>
 #include <vector>
 
+struct maybe_error {
+    bool did_err{false};
+    ValidationInvalidReason reason{ValidationInvalidReason::CONSENSUS};
+    std::string_view error_str;
+
+    constexpr maybe_error() = default;
+    constexpr maybe_error(ValidationInvalidReason reasonIn, std::string_view err): did_err(true), reason(reasonIn), error_str(err) {};
+};
+
 template <typename T>
 inline bool GetTxPayload(const std::vector<unsigned char>& payload, T& obj)
 {

src/evo/specialtxman.cpp

@@ -2,7 +2,7 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
-#include <evo/specialtx.h>
+#include <evo/specialtxman.h>
 
 #include <chainparams.h>
 #include <consensus/validation.h>

src/evo/specialtxman.h

@@ -13,6 +13,9 @@ class CBlock;
 class CBlockIndex;
 class CCoinsViewCache;
 class CValidationState;
+namespace llmq {
+class CQuorumBlockProcessor;
+} // namespace llmq
 
 extern CCriticalSection cs_main;