fix(tooltip): allow multiple tooltips per grid cell

[ghiscoding]

• prior to this PR, we could only have 1 tooltip per cell, but in some occasions, we might have a cell with multiple icons & tooltips, if that happens then we should have separate tooltips (with their dedicated & different tooltipt text) positioned on that inner icon

TODOs

• possibly reposition the arrow at the mouse location?
• possibly center tooltip with center of target element?
• test with multiple tooltips for header row/filter row elements as well
  • this actually requires new SlickEvents because the existing events for header/headerRow are using mouseenter but we need mouseover to differentiate multiple tooltip within the same header (mouseenter only gets triggered once while mouseover gets triggered multiple times while hovering any of element within container). So instead of possible chaning the previous behavior, I decided to duplicate onHeaderMouseEnter to onHeaderMouseOver and the same goes for onHeaderRowMouseEnter and also ...MouseOut for both header types too (so adding 4 new events to cover all use cases). The funny thing is that the event for the cell onMouseEnter is actually using mouseover which is not actually matching with its name.
• add new option to align tooltip to target element (default to false unless we have multiple tooltips, in that case it's always true)
• unit test coverage
• E2E test coverage

for now the POC is mostly working, note that I purposely set a negative top margin in order to also test tooltip that can sometime show at the bottom (in 95% of the case it's showing on top except when there's not enough space on top)

Example 22 (align right)

Example 11 (align left)

Example 12 (multiple tooltips in header row)

existing bugs

• found existing bug when opening slider editor (not a new bug, this one existed before opening this PR)
  
• another bug when tooltip text is too wide, we should use text overflow ellipsis
  

[stackblitz]

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[ghiscoding]

@zewa666 I got a POC mostly working, however I did find some separate/existing bugs with the tooltip plugin and I have identified a few things to potentially do and new options to add in the TODOs list above. Feel free to provide feedback, you could also give it a try by using this awesome new individual PR Stackblitz link.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.8%. Comparing base (863933f) to head (2c3e67f).

Additional details and impacted files

@@           Coverage Diff            @@
##           master   #1448     +/-   ##
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+ Coverage    99.8%   99.8%   +0.1%     
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  Files         199     199             
  Lines       21621   21682     +61     
  Branches     7236    7123    -113     
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+ Hits        21557   21618     +61     
+ Misses         64      58      -6     
- Partials        0       6      +6     

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