⚗ [RUMF-1379] heatmap: experiment improved selector regarding unicity

[BenoitZugmeyer]

Motivation

Improve CSS selector quality for heatmaps

Changes

Add new heatmap CSS selector experiments:

• one stopping the recursion as soon as the selector matches a single element on the page
• one using combined selectors (ex: div > span) to test for unicity to reduce the need of relying on :nth-of-type selectors.
• and a third to test both approaches together.

Testing

• Local
• Staging
• Unit
• End to end

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I have gone over the contributing documentation.

[codecov-commenter]

Codecov Report

Merging #1741 (de8792e) into main (1bf03b1) will increase coverage by 0.00%.
The diff coverage is 96.96%.

@@           Coverage Diff           @@
##             main    #1741   +/-   ##
=======================================
  Coverage   90.71%   90.71%           
=======================================
  Files         130      130           
  Lines        5049     5060   +11     
  Branches     1140     1146    +6     
=======================================
+ Hits         4580     4590   +10     
- Misses        469      470    +1     

Impacted Files	Coverage Δ
...EventsCollection/action/getSelectorsFromElement.ts	98.73% <96.96%> (-1.27%)	⬇️

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