Improve linear tick generators collision estimation

[kurkle]

Resolves #8982

Roughly estimate the space needed for min/max tick in scale units.

• scale_range / (width / font.lineHeight / 0.7) * number_of_digits for horizontal,
• scale_range / (height / fint.lineHeight) for vertical

I'm sure this won't work with all fonts, but its a lot closer to the truth than previous estimation, which is based on the number of spaced between ticks, and does not take the font or chart dimensions into account at all.

0.7 is a quick estimation on the width/height ratio of a digit in average font.

[kurkle]

Filename	Size	Change
dist/chart.esm.js	69.8 kB	+122 B (0%)
dist/chart.js	88.5 kB	+126 B (0%)
dist/chart.min.js	63.1 kB	+99 B (0%)

[etimberg]

Looks good to me. Only risk is if the font size is scriptable, the heuristic breaks down, but that's a very slow case to deal with.