Improve randomness of Password Generator

[DavisNT]

Pull request type

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• Bugfix
• New feature or enhancement
• UI change (please include screenshot!)
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
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What is the current behavior?

Currently when inserting a new character in the password string all selected character classes (uppercase letters, lowercase letters, digits and special characters) are picked first, then within the picked character class a specific character is picked.
This leads to passwords being skewed towards characters from smaller classes. I.e. the probability of a character from a smaller (containing less characters) character class to appear in the password is higher. This is skewed even more by exclusions.

This can be tested by opening Password Generator, selecting Lowercase characters, Uppercase characters and Digit characters, and typing "234567890" (without quotes) in ExcludedCharacters field, and generating 10 passwords of 100 characters each. It should be very visible that around 1/3 of the characters in the generated passwords is the digit 1.

Issue Number: N/A

What is the new behavior?

When inserting a new character in the password string the character is picked from a string containing all the non-excluded characters from all the selected character classes hence the probability of any character being picked is equal.

Other information

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