Update `FontSizeOption` documentation

[Semigradsky]

https://ckeditor.com/docs/ckeditor5/35.2.1/api/module_font_fontsize-FontSizeOption.html

According to example in CKEditor 5 documentation (35.2.1), upcastAlso and view are optional:

const fontSizeConfig = {
    options: [
        {
            title: 'Small',
            model: '8px'
        },
        'default',
        {
            title: 'Big',
            model: '14px'
        }
    ]
};

Related ticket: https://github.com/DefinitelyTyped/DefinitelyTyped/issues/63059

[Semigradsky]

As I see, upcastAlso is marked as optional https://github.com/ckeditor/ckeditor5/blob/656057f3b1e810eb088d1752952dbd99815f8ac0/packages/ckeditor5-font/src/fontsize.js#L61

But it doesn't look as optional in docs:

Smth wrong with the documentation generator?

[CKEditorBot]

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[Semigradsky]

Still valid

[Witoso]

Looks like an invalid doc comment.