Fix ticks.minor and ticks.major configuration issues

[nagix]

This is a fork from #5961 separating the major/minor tick config issues from the rotation and label layout issues.

Problems

1. Can't update scale.ticks.* options at runtime because the scale class copies the minor and major ticks options from ticks.* on the initial chart creation, and it doesn’t update them on the following update calls as the values already exist ([BUG] Can't update scale.ticks.* options at runtime since 2.7.0 #4896).
2. ticks.major.enabled is set to false by default, but ticks.major options are effective. The behavior should be consistent with the ticks.major.enabled setting.

Solutions

1. Deprecates mergeTicksOptions and adds parseTickFontOptions to parse minor and major tick font options. Omitted options are inherited from ticks at runtime.
2. Uses minor tick options when ticks.major.enabled is false.

Master: https://jsfiddle.net/nagix/76fLvg8u/

This PR: https://jsfiddle.net/nagix/4n5rd2gz/

Fixes #4896

[benmccann]

Thanks for splitting up the PRs. It's much easier to review this way.

I noticed that mergeTicksOptions is called in the time scale. I'm not sure why that is or why it's called both there and in buildOrUpdateControllers. It doesn't seem like logic that should be specific to the time scale and can be removed.

[nagix]

Regarding mergeTicksOptions, should we remove it completely in v3?

[simonbrunel]

@nagix Looks great, anything else before merging?

[nagix]

No, this is ready to merge.