make LineHeight::to_absolute take impl Into<Pixels>

[mfreeborn]

Closes discord discussion

[hecrj]

What is the use case? This is a rather internal function.

[mfreeborn]

The exact line of code is:

let text_content = column![current_version_text, next_version_text]
    .spacing(text::LineHeight::default().to_absolute(DEFAULT_FONT_SIZE.into()) / 2.0);

in which I'm setting the spacing of two pieces of text in a column relative to their font size.

i.e. calculating a visually appealing line spacing for these two lines:

[hecrj]

Any reason you are not using text!("...\n...")?

[mfreeborn]

Err, yea I could do that..!