Update @mui/x-date-pickers and Project Schedule settings

[imnasnainaec]

This is prerequisite for installing material-react-table for #2875

Changes:

• install @mui/x-date-pickers (v6)
  • update frontend license report
• replace English-stuck component-specific LocalizationProvider wrappers with one DatePickersLocalizationProvider in AppLoggedIn
  • use current i18next language in DatePickersLocalizationProvider
  • add LocalizationProvider to the ProjectSettings tests (now necessary for the schedule settings with mui/x-date-pickers components without their own providers)
• replace deprecated CalendarPicker with DateCalendar
  • remove unnecessary date and onChange props
  • update prop defaultCalendarMonth to referenceDate
  • replace deprecated renderDay with corresponding usage of slots and slotProps
  • extract two instances of customDayRenderer for a common ProjectPickersDay component
• remove style={{ width: 100 }} from button-holding Grids (sizing that assumed English ui)
• add useEffect with Modal.setAppElement("body"); to prevent a console error

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This change is 

[codecov-commenter]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (11523e3) 72.56% compared to head (911805f) 72.61%.

Files	Patch %	Lines
...components/App/DatePickersLocalizationProvider.tsx	0.00%	2 Missing ⚠️
...jectSettings/ProjectSchedule/ProjectPickersDay.tsx	85.71%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2876      +/-   ##
==========================================
+ Coverage   72.56%   72.61%   +0.04%     
==========================================
  Files         262      264       +2     
  Lines        9976     9972       -4     
  Branches     1163     1162       -1     
==========================================
+ Hits         7239     7241       +2     
+ Misses       2398     2391       -7     
- Partials      339      340       +1     

Flag	Coverage Δ
backend	83.36% <ø> (ø)
frontend	62.60% <76.92%> (+0.08%)	⬆️

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[jasonleenaylor]

After class comment on ProjectPickersDayf

Reviewed 1 of 7 files at r1, 8 of 8 files at r2, all commit messages.
Reviewable status: 9 of 11 files reviewed, all discussions resolved (waiting on @imnasnainaec)

[imnasnainaec]

Added.

Reviewable status: 8 of 11 files reviewed, all discussions resolved (waiting on @imnasnainaec and @jasonleenaylor)

[jasonleenaylor]

Reviewed 2 of 7 files at r1, 1 of 1 files at r3, 1 of 1 files at r4, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @imnasnainaec)