Update feature/secret-hiding with more recent iterations of patch seires

[roypat]

Upgrade the base "mmap support for guest_memfd" series from Fuad's v4 to v12, and do all the Firecracker changes that come with it.

License Acceptance

By submitting this pull request, I confirm that my contribution is made under
the terms of the Apache 2.0 license. For more information on following Developer
Certificate of Origin and signing off your commits, please check
CONTRIBUTING.md.

PR Checklist

• I have read and understand CONTRIBUTING.md.
• I have run tools/devtool checkstyle to verify that the PR passes the
  automated style checks.
• I have described what is done in these changes, why they are needed, and
  how they are solving the problem in a clear and encompassing way.
• I have updated any relevant documentation (both in code and in the docs)
  in the PR.
• I have mentioned all user-facing changes in CHANGELOG.md.
• If a specific issue led to this PR, this PR closes the issue.
• When making API changes, I have followed the
  Runbook for Firecracker API changes.
• I have tested all new and changed functionalities in unit tests and/or
  integration tests.
• I have linked an issue to every new TODO.

---

• This functionality cannot be added in rust-vmm.

[codecov]

Codecov Report

Attention: Patch coverage is 18.18182% with 9 lines in your changes missing coverage. Please review.

Project coverage is 81.76%. Comparing base (0f6b759) to head (a33921e).

Files with missing lines	Patch %	Lines
src/vmm/src/builder.rs	10.00%	9 Missing ⚠️

Additional details and impacted files

@@                    Coverage Diff                    @@
##           feature/secret-hiding    #5293      +/-   ##
=========================================================
+ Coverage                  81.63%   81.76%   +0.13%     
=========================================================
  Files                        250      250              
  Lines                      27666    27650      -16     
=========================================================
+ Hits                       22584    22608      +24     
+ Misses                      5082     5042      -40     

Flag	Coverage Δ
5.10-c5n.metal	81.94% <18.18%> (+<0.01%)	⬆️
5.10-m5n.metal	81.94% <18.18%> (+0.01%)	⬆️
5.10-m6a.metal	81.10% <18.18%> (+<0.01%)	⬆️
5.10-m6g.metal	77.92% <18.18%> (+0.02%)	⬆️
5.10-m6i.metal	81.93% <18.18%> (+<0.01%)	⬆️
5.10-m7a.metal-48xl	81.08% <18.18%> (?)
5.10-m7g.metal	77.92% <18.18%> (+0.02%)	⬆️
5.10-m7i.metal-24xl	81.90% <18.18%> (?)
5.10-m7i.metal-48xl	81.89% <18.18%> (?)
5.10-m8g.metal-24xl	77.91% <18.18%> (?)
5.10-m8g.metal-48xl	77.91% <18.18%> (?)
6.1-c5n.metal	81.97% <18.18%> (-0.01%)	⬇️
6.1-m5n.metal	81.98% <18.18%> (+<0.01%)	⬆️
6.1-m6a.metal	81.14% <18.18%> (+<0.01%)	⬆️
6.1-m6g.metal	77.92% <18.18%> (+0.02%)	⬆️
6.1-m6i.metal	81.97% <18.18%> (-0.01%)	⬇️
6.1-m7a.metal-48xl	81.13% <18.18%> (?)
6.1-m7g.metal	77.92% <18.18%> (+0.02%)	⬆️
6.1-m7i.metal-24xl	81.99% <18.18%> (?)
6.1-m7i.metal-48xl	81.99% <18.18%> (?)
6.1-m8g.metal-24xl	77.91% <18.18%> (?)
6.1-m8g.metal-48xl	77.91% <18.18%> (?)
6.14-c5n.metal	82.02% <18.18%> (?)
6.14-m5n.metal	82.02% <18.18%> (?)
6.14-m6a.metal	81.18% <18.18%> (?)
6.14-m6g.metal	77.95% <18.18%> (?)
6.14-m6i.metal	82.01% <18.18%> (?)
6.14-m7a.metal-48xl	81.17% <18.18%> (?)
6.14-m7g.metal	77.96% <18.18%> (?)
6.14-m7i.metal-24xl	82.03% <18.18%> (?)
6.14-m7i.metal-48xl	82.03% <18.18%> (?)
6.14-m8g.metal-24xl	77.95% <18.18%> (?)
6.14-m8g.metal-48xl	77.95% <18.18%> (?)

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