[MWPW-140627] [MEP] Replace MEP placeholders when loading fragments

[AdobeLinhart]

When we insert text/HTML in MEP, we call the replacePlaceholders function to replace any already known placeholders (aka MEP placeholders).  We want to do the same thing when it's fragment content that has a MEP placeholder.  So we'll want to call that function again from fragments.js

At the end of fragments.js init function, we are calling handleMepCommands. Afterwards, I think we should test for config.placeholders and fragment's html having a placeholder.  If so, run it through replacePlaceholders.

Note, since there were now 3 if statements that all repeated importing personalization.js for 3 different functions, they were moved to all be nested inside 1 if.

QA instructions
The main element on the test page only uses MEP placeholders, but the gnav also uses regular placeholders. To test this PR, check the performance tab in dev tools for the before and after links. Not only should the LCP be much faster, but it should not call placeholders.json until after LCP in the after link.

Resolves: MWPW-140627

Test URLs:

• Before: https://main--cc--adobecom.hlx.page/drafts/mepdev/fragments/2024/q4/fragmentplaceholders/marquee
• After: https://main--cc--adobecom.hlx.page/drafts/mepdev/fragments/2024/q4/fragmentplaceholders/marquee?milolibs=fragmentplaceholders
• Psi: https://fragmentplaceholders--milo--adobecom.hlx.page/?martech=off

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Commits

• 98c87a3 ✅ (latest)
• 6283687 ✅

[aem-code-sync]

	Page	Scores	Audits	Google
📱	/?martech=off
🖥️	/?martech=off

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.36%. Comparing base (1fa592a) to head (98c87a3).
Report is 579 commits behind head on stage.

Additional details and impacted files

@@            Coverage Diff             @@
##            stage    #3193      +/-   ##
==========================================
+ Coverage   95.69%   96.36%   +0.67%     
==========================================
  Files         165      245      +80     
  Lines       43542    56610   +13068     
==========================================
+ Hits        41668    54554   +12886     
- Misses       1874     2056     +182     

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[github-actions]

Reminder to set the Ready for Stage label - to queue this to get merged to stage & production.