fuzz: wallet: add target for CreateTransaction

[brunoerg]

This PR adds a fuzz target for the CreateTransaction function. It is a regression target for #27271 and can be testing by applying:

@@ -1110,7 +1110,7 @@ static util::Result<CreatedTransactionResult> CreateTransactionInternal(
     // This can only happen if feerate is 0, and requested destinations are value of 0 (e.g. OP_RETURN)
     // and no pre-selected inputs. This will result in 0-input transaction, which is consensus-invalid anyways
     if (selection_target == 0 && !coin_control.HasSelected()) {
-        return util::Error{_("Transaction requires one destination of non-0 value, a non-0 feerate, or a pre-selected input")};
+       // return util::Error{_("Transaction requires one destination of non-0 value, a non-0 feerate, or a pre-selected input")};
     }

Also, it moves ImportDescriptors function to src/wallet/test/util.h to avoid to duplicate same code.

[DrahtBot]

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Conflicts

Reviewers, this pull request conflicts with the following ones:

• #29564 (wallet: clarify FundTransaction signature by S3RK)
• #22838 (descriptors: Be able to specify change and receiving in a single descriptor string by achow101)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

[brunoerg]

cc: @maflcko

[maflcko]

lgtm, nice!

[brunoerg]

Rebased