fa1c8e297 Resolve the qt/guiutil <-> qt/optionsmodal CD (251)
Pull request description:
This pull request attempts to resolve the `qt/guiutil` <-> `qt/optionsmodel` circular dependency.
The `Intro` class in `qt/intro` has a static member function `getDefaultDataDirectory` which is used by `qt/optionsmodel` and creates the circular dependency
`qt/guiutil -> qt/walletmodel -> qt/optionsmodel -> qt/intro -> qt/guiutil`.
This circular dependency is resolved by moving `Intro::getDefaultDataDirectory` to `GUIUtil::getDefaultDataDirectory` without modifying the implementation.
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Backport of Core PR15874