PR: Try calling newer Qt methods first before falling back to deprecated/removed ones

[kumattau]

Hi,

This PR makes new APIs priority use than removed or deprecated APIs to solves the following DeprecationWarnings of qtabrowser with QT_API=pyside2 or QT_API=pyside6.

QT_API=pyside2

qtawesome/icon_browser.py:125: DeprecationWarning: QDesktopWidget.screenNumber(const QPoint & arg__1) const is deprecated
  screen = desktop.screenNumber(desktop.cursor().pos())
qtawesome/qtawesome/icon_browser.py:126: DeprecationWarning: QDesktopWidget.screenGeometry(int screen) const is deprecated
  centerPoint = desktop.screenGeometry(screen).center()

QT_API=pyside6

qtawesome/icon_browser.py:273: DeprecationWarning: 'exec_' will be removed in the future. Use 'exec' instead.
  sys.exit(app.exec_())

• exec_ function is handled as discussed in https://github.com/spyder-ide/qtpy/issues/286
• Additionally, new set Filter Regular Expression is priority used than removed setFilterRegExp considering the possibility that PySide2/PyQt5 will report DeprecationWarning in the future.

I tested that this PR with the current master branch of QtPy (https://github.com/spyder-ide/qtpy/commit/53ce7b00f6cd90eb45e2b78bed953671841d4899) reports no DeprecationWarning on the following environments.

PySide2                    5.15.2
PySide6                    6.2.1

PyQt5                      5.15.6
PyQt5-Qt5                  5.15.2
PyQt5-sip                  12.9.0
PyQt5-stubs                5.15.2.0

PyQt6                      6.2.0
PyQt6-Qt6                  6.2.0
PyQt6-sip                  13.1.0

pyqt                      5.9.2            py36h05f1152_2
qt                        5.9.7                h5867ecd_1
sip                       4.19.8           py36hf484d3e_0

[kumattau]

I rebased onto master.

[kumattau]

Thank @dalthviz for review. I updated the commit.

• keep sys.exit(app.exec_())
• change commit message to PR title