Add height, depth, and hash methods to the Chain interface

And use them to remove uses of chainActive and mapBlockIndex in wallet code

This commit does not change behavior.

Co-authored-by: Ben Woosley <ben.woosley@gmail.com>

src/interfaces/chain.cpp

@@ -4,7 +4,9 @@
 
 #include <interfaces/chain.h>
 
+#include <chain.h>
 #include <sync.h>
+#include <uint256.h>
 #include <util/system.h>
 #include <validation.h>
 
@@ -16,6 +18,34 @@ namespace {
 
 class LockImpl : public Chain::Lock
 {
+    Optional<int> getHeight() override
+    {
+        int height = ::chainActive.Height();
+        if (height >= 0) {
+            return height;
+        }
+        return nullopt;
+    }
+    Optional<int> getBlockHeight(const uint256& hash) override
+    {
+        CBlockIndex* block = LookupBlockIndex(hash);
+        if (block && ::chainActive.Contains(block)) {
+            return block->nHeight;
+        }
+        return nullopt;
+    }
+    int getBlockDepth(const uint256& hash) override
+    {
+        const Optional<int> tip_height = getHeight();
+        const Optional<int> height = getBlockHeight(hash);
+        return tip_height && height ? *tip_height - *height + 1 : 0;
+    }
+    uint256 getBlockHash(int height) override
+    {
+        CBlockIndex* block = ::chainActive[height];
+        assert(block != nullptr);
+        return block->GetBlockHash();
+    }
 };
 
 class LockingStateImpl : public LockImpl, public UniqueLock<CCriticalSection>