autotests: test TextFieldContextMenu

Setting TapHandler's longPressThreshold to 0 will disable the longPressed signal since Qt 6.6.2, which breaks the text context menu again. This adds a test to make sure the menu can be opened, and catch potential regressions caused by upstream changes in the future.

CCBUG: 481293
CCQTBUG: https://bugreports.qt.io/browse/QTBUG-119132