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]

There has been no activity on this issue for the past year. We've marked it as stale and will close it in 30 days. We understand it may still be relevant, so if you're interested in the solution, leave a comment or reaction under this issue.

[Semigradsky]

Still valid

[Witoso]

Looks like an invalid doc comment.

[CKEditorBot]

There has been no activity on this issue for the past year. We've marked it as stale and will close it in 30 days. We understand it may still be relevant, so if you're interested in the solution, leave a comment or reaction under this issue.

[Semigradsky]

Still valid

[CKEditorBot]

There has been no activity on this issue for the past year. We've marked it as stale and will close it in 30 days. We understand it may still be relevant, so if you're interested in the solution, leave a comment or reaction under this issue.

[CKEditorBot]

We've closed your issue due to inactivity. We understand that the issue may still be relevant. If so, feel free to open a new one (and link this issue to it).