MWPW-158674 [MEP] Support nested placholders in MEP placeholders

[vgoodric]

• Support using a MEP placeholder in a MEP placeholder.

Resolves: MWPW-158674

Sample page tests:

1. the nested placeholder being before, after or in a different manifest than the one that uses it
2. a nested placeholder is defined twice and the last definition is used

QA instructions:
H1 should read: Buy now and save 50% off CC All Apps.
Description should start with: For just US$49.99,

Test URLs:

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

Also includes #2919 for conflict resolution

[aem-code-sync]

Hello, I'm the AEM Code Sync Bot and I will run some actions to deploy your branch and validate page speed.
In case there are problems, just click a checkbox below to rerun the respective action.

• Re-run PSI checks
• Re-sync branch

Commits

• 130b5e0 ✅ (latest)
• 71416c8 ✅
• 04cf9f8 ✅
• 79c1e90 ✅
• d63a9e3 ✅
• 7d2dc34 ✅

[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 96.24%. Comparing base (c3c9bcc) to head (130b5e0).
Report is 1 commits behind head on stage.

Additional details and impacted files

@@           Coverage Diff           @@
##            stage    #2908   +/-   ##
=======================================
  Coverage   96.24%   96.24%           
=======================================
  Files         236      236           
  Lines       54254    54278   +24     
=======================================
+ Hits        52217    52241   +24     
  Misses       2037     2037           

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[github-actions]

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