feat(common)!: migrate from Flatpickr to Vanilla-Calendar

[ghiscoding]

• The reason to migrate away from Flatpickr is mostly because it's barely supported anymore (no PRs were merged since well over 2 years), it doesn't offer full ESM support and styling could be a bit more modern (the use of default select, inputs to change year/month/time is a bit outdated and rudimentary and finally date range selection could also be improved).
• Vanilla-Calendar-Pro offers most of that even though it has some rough corners, the biggest con to this new lib is the use of template with HTML strings (dropping CSP support), and it seems to takes a few weeks to accept any PRs, so I might end up forking it, we'll see... but nonetheless I find it's a great upgrade and it also offers a nice Dark Mode by default and the locale support is flawless and uses simple, but clever, native code without even needing any locale files.
  • went ahead with a new fork named vanilla-calendar-picker
• this migration also offers much smaller build size
• this is a breaking change and is only targeted for the next major version

TODOs

• update all unit tests with full coverage (currently failing because an issue that was fixed via a PR waiting to be merged)
  • might need to pnpm patch it until my PR is merged on that repo, so that my unit tests could run
• update all Cypress tests
• remove previous Flatpickr styling
• remove previous Flatpickr Docs
• add missing auto-positioning (top/bottom)
• test in downstream repos like Angular-Slickgrid
• add build size comparison reference

Build Size Comparison

File	before	after	diff	% diff
SF Bundle Zip File	582Kb (596,143)	565Kb (579,246)	-17Kb	2.83% smaller
GitHub Vite Demo Website	5.12Mb (5,376,179)	5.16Mb (5,415,631)	+39Kb	0.7% larger

NOTE actually it turns out that after the Vanilla-Calendar migration, the build is larger not smaller (as seen in the demo build) and the reason was because the CSS file wasn't properly loaded which made it looks like it was smaller but in fact is larger.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.8%. Comparing base (12661a3) to head (e0180d3).

Additional details and impacted files

@@           Coverage Diff           @@
##            next   #1466     +/-   ##
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+ Coverage   99.8%   99.8%   +0.1%     
=======================================
  Files        199     199             
  Lines      21763   21766      +3     
  Branches    7264    7249     -15     
=======================================
+ Hits       21699   21702      +3     
  Misses        58      58             
  Partials       6       6             

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[ghiscoding]

Alright, I think this is ready to be merged and move to next phase :)