Merge bitcoindevkit/bdk#682: Add a custom signer for hardware wallets

138acc3b7d Change `populate_test_db` to not return empty input (wszdexdrf)
d6e1dd1040 Change CI to add test using ledger emulator (wszdexdrf)
76034772cb Add a custom signer for hardware wallets (wszdexdrf)

Pull request description:

  Also adds a new test in CI for building and testing on a virtual
  hardware wallet.

  ### Description

  This PR would enable BDK users to sign transactions using a hardware wallet. It is just the beginning hence there are no complex features, but I hope not for long.
  I have added a test in CI for building a ledger emulator and running the new test on it. The test is similar to the one on bitcoindevkit/rust-hwi.

  ### Notes to the reviewers
  The PR is incomplete (and wouldn't work, as the rust-hwi in `cargo.toml` is pointing to a local crate, temporarily) as a small change is required in rust-hwi (https://github.com/bitcoindevkit/rust-hwi/pull/42).

  ### Checklists

  #### All Submissions:

  * [x] I've signed all my commits
  * [x] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk/blob/master/CONTRIBUTING.md)
  * [x] I ran `cargo fmt` and `cargo clippy` before committing

  #### New Features:

  * [x] I've added tests for the new feature
  * [x] I've added docs for the new feature
  * [x] I've updated `CHANGELOG.md`

ACKs for top commit:
  afilini:
    ACK 138acc3b7d

Tree-SHA512: 54337f06247829242b4dc60f733346173d957de8e9f8b80beb91304d679cfb4e0e4db722c967469265a5b6ede2bd641ba5c089760391c671995dc30de37897de

src/database/memory.rs

@@ -491,11 +491,10 @@ macro_rules! populate_test_db {
         let mut db = $db;
         let tx_meta = $tx_meta;
         let current_height: Option<u32> = $current_height;
-        let input = if $is_coinbase {
-            vec![$crate::bitcoin::TxIn::default()]
-        } else {
-            vec![]
-        };
+        let mut input = vec![$crate::bitcoin::TxIn::default()];
+        if !$is_coinbase {
+            input[0].previous_output.vout = 0;
+        }
         let tx = $crate::bitcoin::Transaction {
             version: 1,
             lock_time: 0,