pyinstaller build: towards fixing missing "gui/common_qt" folder

pyinstaller tries to import electrum and its different submodules at build-time
during the "Analysis" phase. sys._GUI_QT_VERSION was not getting set there,
and the resulting exception was blocking pyinstaller from discovering that
gui/common_qt is being used.

at runtime:
```
$ ./dist/Electrum.app/Contents/MacOS/run_electrum
  1.53 | E | daemon.Daemon | GUI raised exception: Exception('Error loading trustedcoin plugin: ModuleNotFoundError("No module named \'electrum.gui.common_qt\'")'). shutting down.
  1.53 | E | __main__ | daemon.run_gui errored
Traceback (most recent call last):
  File "electrum/plugin.py", line 135, in load_plugin
    spec.loader.exec_module(module)
  File "<frozen importlib._bootstrap_external>", line 883, in exec_module
  File "<frozen importlib._bootstrap>", line 241, in _call_with_frames_removed
  File "/Users/vagrant/electrum/dist/Electrum.app/Contents/MacOS/electrum/plugins/trustedcoin/qt.py", line 51, in <module>
    from .common_qt import TrustedcoinPluginQObject
  File "/Users/vagrant/electrum/dist/Electrum.app/Contents/MacOS/electrum/plugins/trustedcoin/common_qt.py", line 16, in <module>
    from electrum.gui.common_qt.plugins import PluginQObject
ModuleNotFoundError: No module named 'electrum.gui.common_qt'

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "run_electrum", line 456, in handle_cmd
    d.run_gui()
  File "electrum/daemon.py", line 617, in run_gui
    self.gui_object = gui.ElectrumGui(config=self.config, daemon=self, plugins=self._plugins)
  File "electrum/util.py", line 473, in do_profile
    o = func(*args, **kw_args)
  File "electrum/gui/qt/__init__.py", line 153, in __init__
    self.plugins.load_plugin('trustedcoin')
  File "electrum/plugin.py", line 138, in load_plugin
    raise Exception(f"Error loading {name} plugin: {repr(e)}") from e
Exception: Error loading trustedcoin plugin: ModuleNotFoundError("No module named 'electrum.gui.common_qt'")
```

contrib/build-wine/deterministic.spec

@@ -62,6 +62,7 @@ a = Analysis([home+'run_electrum',
               home+'electrum/bitcoin.py',
               home+'electrum/dnssec.py',
               home+'electrum/commands.py',
+              home+'electrum/plugins/trustedcoin/qt.py',
               home+'electrum/plugins/cosigner_pool/qt.py',
               home+'electrum/plugins/trezor/qt.py',
               home+'electrum/plugins/safe_t/client.py',

contrib/osx/osx.spec

@@ -67,6 +67,7 @@ a = Analysis([electrum+ MAIN_SCRIPT,
               electrum+'electrum/bitcoin.py',
               electrum+'electrum/dnssec.py',
               electrum+'electrum/commands.py',
+              electrum+'electrum/plugins/trustedcoin/qt.py',
               electrum+'electrum/plugins/cosigner_pool/qt.py',
               electrum+'electrum/plugins/trezor/qt.py',
               electrum+'electrum/plugins/safe_t/client.py',

electrum/gui/common_qt/__init__.py

@@ -0,0 +1,16 @@
+# Copyright (C) 2023 The Electrum developers
+# Distributed under the MIT software license, see the accompanying
+# file LICENCE or http://www.opensource.org/licenses/mit-license.php
+
+import sys
+
+
+# FIXME: remove when both desktop and mobile are Qt6
+def get_qt_major_version() -> int:
+    _GUI_QT_VERSION = getattr(sys, '_GUI_QT_VERSION', None)
+    if _GUI_QT_VERSION is None:
+        # used by pyinstaller when building (analysis phase)
+        _GUI_QT_VERSION = 5
+    if _GUI_QT_VERSION in (5, 6):
+        return _GUI_QT_VERSION
+    raise Exception(f"unexpected {_GUI_QT_VERSION=}")

electrum/gui/common_qt/plugins.py

@@ -1,9 +1,13 @@
 import sys
 
-if getattr(sys, '_GUI_QT_VERSION') == 5:  # FIXME: remove when both desktop and mobile are Qt6
+from . import get_qt_major_version
+
+if (qt_ver := get_qt_major_version()) == 5:
     from PyQt5.QtCore import pyqtSignal, pyqtProperty, QObject
-else:
+elif qt_ver == 6:
     from PyQt6.QtCore import pyqtSignal, pyqtProperty, QObject
+else:
+    raise Exception(f"unexpected {qt_ver=}")
 
 from electrum.logging import get_logger
 

electrum/plugins/trustedcoin/common_qt.py

@@ -4,10 +4,14 @@ import base64
 import sys
 from typing import TYPE_CHECKING
 
-if getattr(sys, '_GUI_QT_VERSION') == 5:  # FIXME: remove when both desktop and mobile are Qt6
+from electrum.gui.common_qt import get_qt_major_version
+
+if (qt_ver := get_qt_major_version()) == 5:
     from PyQt5.QtCore import pyqtSignal, pyqtProperty, pyqtSlot
-else:
+elif qt_ver == 6:
     from PyQt6.QtCore import pyqtSignal, pyqtProperty, pyqtSlot
+else:
+    raise Exception(f"unexpected {qt_ver=}")
 
 from electrum.i18n import _
 from electrum.bip32 import BIP32Node