Slider with dynamic ticks and labels

Pseudo-pull request:
I moved the code initializing the slider’s min/max values etc. to the slider’s form_show (rather than the Main form’s form_show in the demo) so that the behavior is as (I) expected when using the slider component elsewhere.
https://anvil.works/build#clone:Y5LUOEM5XWUSFREF=JMXUOTMM47I5ZPIPFLQFQYEK