Fix computation of X axis ticks angle

[benoitbzl]

Use the tick formating function to compute the X axis ticks angle.

What kind of change does this PR introduce? (check one with "x")

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior? (You can also link to an open issue here)
We are using our own X tick formatting function which reduces a date to "month/day" format, but the actual code does not use this function to compute the x axis tick angle. In our case, the tick text should not be rotated but the current implementation produces an angle of -30 or -60 deg instead.
Moreover, as a side effect, we are seeing a flickering of the line chart, as the angle changes between -30 and -60 deg continuously.

What is the new behavior?

The x axis tick angle is computed accordingly to the tick string displayed.

Does this PR introduce a breaking change? (check one with "x")

• Yes
• No

If this PR contains a breaking change, please describe the impact and migration path for existing applications: ...
N/A

Other information:

[marjan-georgiev]

Looks good, thank you!