Make PasswordBox follow user set height.

The widgets in PasswordBox have a fixed height in them. This means that if some theme applies a custom height to PasswordBox, it is ignored, and the default 30px is used anyway.

This commit makes it so the widgets inside PasswordBox inherit the container's size, so when a custom height is applied, it is followed.

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I have tested the default themes included and they are unaffected by this change.