Merge bitcoin/bitcoin#31603: descriptor: check whitespace in keys within fragments

21e9d39a37 docs: add release notes for 31603 (brunoerg)
a8b548d75d test: `getdescriptorinfo`/`importdescriptors` with whitespace in pubkeys (brunoerg)
c7afca3d62 test: descriptor: check whitespace into keys (brunoerg)
cb722a3cea descriptor: check whitespace in ParsePubkeyInner (brunoerg)
50856695ef test: fix descriptors in `ismine_tests` (brunoerg)

Pull request description:

  Currently, we successfully parse descriptors which contains spaces in the beginning or end of the public/private key within a fragment (e.g. `pk( KEY)`, `pk(KEY )` or `pk( KEY )`). I have noticed that one of the reasons is that the `DecodeBase58` function simply ignore these whitespaces.

  This PR changes the `ParsePubkeyInner ` to reject pubkeys that contain a whitespace at the beginning and/or at the end. We will only check the whitespace in some RPCs (e.g. `importdescriptors`), but an already imported descriptor won't be affected by this check, especially because we store descriptors from `ToString`.

  For context: https://github.com/brunoerg/bitcoinfuzz/issues/72

ACKs for top commit:
  rkrux:
    tACK 21e9d39a37
  darosior:
    re-ACK 21e9d39a37
  sipa:
    utACK 21e9d39a37

Tree-SHA512: 54f48a89a235517e5cdc29a46dceeb7dabbee93c7616a166288ff3f90131808eb0ece43b0797a11fe827a5f7bd51d65e3e75c16789b0a42020934cabb684cc8f

src/script/descriptor.cpp

@@ -1509,6 +1509,10 @@ std::vector<std::unique_ptr<PubkeyProvider>> ParsePubkeyInner(uint32_t key_exp_i
         error = "No key provided";
         return {};
     }
+    if (IsSpace(str.front()) || IsSpace(str.back())) {
+        error = strprintf("Key '%s' is invalid due to whitespace", str);
+        return {};
+    }
     if (split.size() == 1) {
         if (IsHex(str)) {
             std::vector<unsigned char> data = ParseHex(str);