Merge bitcoin/bitcoin#25858: psbt: Only include PSBT_OUT_TAP_TREE when the output has a script path

9e386afb67 tests: Test that PSBT_OUT_TAP_TREE is included correctly (Andrew Chow)
30ff25cf37 psbt: Only include m_tap_tree if it has scripts (Andrew Chow)
0577d423ad psbt: Change m_tap_tree to store just the tuples (Andrew Chow)
22c051ca70 tests: Test that PSBT_OUT_TAP_TREE is combined correctly (Andrew Chow)
7df6e1bb77 psbt: Fix merging of m_tap_tree (Andrew Chow)
0652dc53b2 [BugFix]: Do not allow deserializing PSBT with empty PSBT_OUT_TAP_TREE (Jeremy Rubin)

Pull request description:

  PSBT_OUT_TAP_TREE should not be included for outputs that do not have such a tree. This should be disallowed during parsing, as well as prior to serialization when the field is populated during updating.

  Also added some test cases.

  Alternative to #25856

ACKs for top commit:
  instagibbs:
    ACK 9e386afb67
  darosior:
    ACK 9e386afb67

Tree-SHA512: ce5c02a69752d176dbd967c1e8d30129b1905c8f186aeeef034576c1de82059271a1ee846bd040f5be4e66bb77ba711dcf14ac1e597c5707d7e7e2293f6cfefb

src/script/standard.h

@@ -315,6 +315,8 @@ public:
     TaprootSpendData GetSpendData() const;
     /** Returns a vector of tuples representing the depth, leaf version, and script */
     std::vector<std::tuple<uint8_t, uint8_t, CScript>> GetTreeTuples() const;
+    /** Returns true if there are any tapscripts */
+    bool HasScripts() const { return !m_branch.empty(); }
 };
 
 /** Given a TaprootSpendData and the output key, reconstruct its script tree.