API: convert offset/location to TextLocation and vice versa

[rebornix]

Is your feature request related to a problem? Please describe.

TextView currently supports converting offset (Int) to line/column (TextLocation). With this API we could build our own Line/Column status, but if we have a Line/Column there is no API to help convert it to offset.

Describe the solution you'd like

We can have an override of textLocation API so embedders can covert between offset and line/column with the same method.

    public func textLocation(at location: Int) -> TextLocation? {
        if let linePosition = textInputView.linePosition(at: location) {
            return TextLocation(linePosition)
        } else {
            return nil
        }
    }
    
+    public func textLocation(at textLocation: TextLocation) -> Int? {
+        let lineIndex = textLocation.lineNumber
+        
+        guard lineIndex >= 0 && lineIndex < textInputView.lineManager.lineCount else {
+            return nil
+        }
+
+        let line = textInputView.lineManager.line(atRow: lineIndex)
+        return line.location + textLocation.column
+    }

Describe alternatives you've considered

Without this we would need to either calculate line ends ourselves or introduce "proxy functions" (like GoToLine).

[simonbs]

This sounds like a good addition. Are you up for creating a PR?

Before doing line.location + textLocation.column we might want to check that the resulting location is within the bounds of the line and return nil otherwise. I haven't tested it but something like the following guard should do the trick.

guard textLocation.column >= 0 && textLocation.column <= line.data.totalLength else {
    return nil
}