3.16 - Improve the LCP/ATF detection of the beacon script

[MathieuLamiot]

Context @mostafa-hisham already tried to run an equivalent of the beacon script on the SaaS and prepared some enhancements to make the script more reliable, more efficient and accurate: see his comments on this PR.

Expected behavior Implement the enhancements listed by @mostafa-hisham in this PR:

• https://github.com/wp-media/wp-rocket/issues/6513
• #6514
• #6515
• #6522
• #6543

Additional information This issue originates from the discussions here

[remyperona]

This one is out of my skillset to handle

[Miraeld]

It's also out of mine...