Make tableViewStyle public

[ChaosCoder]

This PR makes it possible for subclasses of FormViewController to specify a UITableView.Style for the form table.

This way, a subclass can specify the style e.g. via the initializer called by UIKit:

required init?(coder aDecoder: NSCoder) {
    super.init(coder: aDecoder)
    tableViewStyle = .plain
}

or lets you specify the style in viewDidLoad:

override func viewDidLoad() {
    if #available(iOS 13.0, *) {
        self.tableViewStyle = .insetGrouped
    }
    
    super.viewDidLoad()
}

Motivation

I needed to be able to set the table view style in viewDidLoad to .insetGrouped in my project but failed at doing so, because the tableViewStyle-property in FormViewController is marked as private.

Changes

This simply marks the property tableViewStyle as public instead of private.