Merge bitcoin-core/gui#686: clang-tidy: Force checks for headers in src/qt

7b7cd11244 clang-tidy, qt: Force checks for headers in `src/qt` (Hennadii Stepanov)
69eacf2c5e clang-tidy, qt: Fix `modernize-use-default-member-init` in headers (Hennadii Stepanov)

Pull request description:

  This PR split from bitcoin/bitcoin#26705 and contains only changes in `src/qt`.

  Effectively, it fixes the clang-tidy's `modernize-use-default-member-init` errors, and forces clang-tidy checks for all headers in the `src/qt` directory.

ACKs for top commit:
  jarolrod:
    ACK 7b7cd11244

Tree-SHA512: 79525bb0f31ae7cad88c781e55091a21467c0485ddc1ed03ad62e051480fda3b3710619ea11af480437edba3c6e038f7c40edc6b373e3a37408c006d11b34686

src/qt/sendcoinsdialog.cpp

@@ -64,11 +64,7 @@ int getIndexForConfTarget(int target) {
 SendCoinsDialog::SendCoinsDialog(const PlatformStyle *_platformStyle, QWidget *parent) :
     QDialog(parent, GUIUtil::dialog_flags),
     ui(new Ui::SendCoinsDialog),
-    clientModel(nullptr),
-    model(nullptr),
     m_coin_control(new CCoinControl),
-    fNewRecipientAllowed(true),
-    fFeeMinimized(true),
     platformStyle(_platformStyle)
 {
     ui->setupUi(this);