Merge #404: Fix various edge case bugs in QValidatedLineEdit

aeb18b6 Bugfix: GUI: Check validity when QValidatedLineEdit::setText is called (Luke Dashjr)
b1a544b Bugfix: GUI: Re-check validity after QValidatedLineEdit::setCheckValidator (Luke Dashjr)
2385b50 Bugfix: GUI: Only apply invalid style to QValidatedLineEdit, not its tooltip (Luke Dashjr)

Pull request description:

  1. Use a CSS selector to avoid changing the background colour of the tooltip.
  2. Re-check validity of input when we first set the validator (probably a no-op in practice).
  3. Check validity of input when it is set programmatically via `setText` (eg, via the address book). Probably no-op in practice UNTIL merging bitcoin/bitcoin#15987 or any other PR that adds a warning for valid addresses.

  Moved from bitcoin/bitcoin#18133 (just concept ACKs)

ACKs for top commit:
  Sjors:
    tACK aeb18b6
  hebasto:
    ACK aeb18b6, tested on Linux Mint 20.3 (Qt 5.12.8).

Tree-SHA512: b6fa8ee4dec76e1c759095721240e6fa5071a02993cb28406e96a0fa2e819f5dddc03d2e7c9073354d7865c2b09eb263afaf853ecba42e9fc4f50ef4ae20bf0f

src/qt/qvalidatedlineedit.cpp

@@ -15,6 +15,12 @@ QValidatedLineEdit::QValidatedLineEdit(QWidget *parent) :
     connect(this, &QValidatedLineEdit::textChanged, this, &QValidatedLineEdit::markValid);
 }
 
+void QValidatedLineEdit::setText(const QString& text)
+{
+    QLineEdit::setText(text);
+    checkValidity();
+}
+
 void QValidatedLineEdit::setValid(bool _valid)
 {
     if(_valid == this->valid)
@@ -28,7 +34,7 @@ void QValidatedLineEdit::setValid(bool _valid)
     }
     else
     {
-        setStyleSheet(STYLE_INVALID);
+        setStyleSheet("QValidatedLineEdit { " STYLE_INVALID "}");
     }
     this->valid = _valid;
 }
@@ -106,6 +112,7 @@ void QValidatedLineEdit::checkValidity()
 void QValidatedLineEdit::setCheckValidator(const QValidator *v)
 {
     checkValidator = v;
+    checkValidity();
 }
 
 bool QValidatedLineEdit::isValid()

src/qt/qvalidatedlineedit.h

@@ -29,6 +29,7 @@ class QValidatedLineEdit : public QLineEdit
     const QValidator *checkValidator;
 
 public Q_SLOTS:
+    void setText(const QString&);
     void setValid(bool valid);
     void setEnabled(bool enabled);