Add 'todayInstantiator' property to allow custom today's Date creation

[jonagoldman]

Fixes #1080 by adding a new todayInstantiator property.

This allows to pass a function like this:

<b-datepicker :today-instantiator="todayInstantiator"></b-datepicker>

todayInstantiator() {
    return new Date()
},

This fixes some issues when the browser default new Date() instantiation used inside the component does not match the way each application works with dates.

For example, in an app that uses Moment or Luxon to set a timezone, the today's date set by the app can be different from the today's date used inside the component.

With this property I have the freedom to do something like this:

todayInstantiator() {
    return moment().tz('Australia/Sydney').toDate()
},

The todayInstantiator property is a function that must always return a regular JS Date object representing today's date.

Please note this function only applies when the component wants to get the today's date using new Date() and does not change anything else, ensuring that nothing breaks.

[codecov]

Codecov Report

Merging #1083 into dev will increase coverage by 0.05%.
The diff coverage is 60%.

@@            Coverage Diff            @@
##             dev    #1083      +/-   ##
=========================================
+ Coverage   42.9%   42.95%   +0.05%     
=========================================
  Files         41       41              
  Lines       1296     1299       +3     
  Branches     403      404       +1     
=========================================
+ Hits         556      558       +2     
- Misses       721      722       +1     
  Partials      19       19

Impacted Files	Coverage Δ
src/utils/config.js	100% <ø> (ø)	⬆️
src/components/datepicker/DatepickerTable.vue	24.13% <ø> (ø)	⬆️
src/components/datepicker/DatepickerTableRow.vue	31.57% <ø> (ø)	⬆️
src/components/datepicker/Datepicker.vue	37.5% <60%> (+1.02%)	⬆️

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[jtommy]

@jonagoldman PR is ok, but i'm not sure about the prop name to be honest

[jonagoldman]

@jtommy I'm not sure either :) First I called it date-instatiator but it's not accureate as it only instantiates today's date. Maybe today-creator, today-date or date-creator ?

[jtommy]

today-date or date-creator, as you want

[jonagoldman]

@jtommy done

[jtommy]

@jonagoldman Thanks

[zedrdave]

If I understand correctly, this would allow displaying the Datepicker in an arbitrary timezone instead of the user local by default?

Would it be possible to add the same parameter to Timepicker, so that it can be available to all components (I'm assuming it would then be possible to use Datetimepicker by providing both parameters to the subcomponents, right?)…

Sorry, please ignore previous paragraph: I hadn't realise the name had been changed to dateCreator and that there was indeed already a datetimeCreator in DatetimePicker!