Yocto 5.3 (whinlatter) migration: CI and recipe updates

[ajlennon]

Summary

Migrate meta-mono to support Yocto 5.3 (whinlatter). The poky repository no longer maintains release branches from whinlatter onwards, requiring a new CI setup approach.

• CI: replace poky clone with individual repo clones -- bitbake (branch 2.16), openembedded-core (whinlatter), meta-yocto (whinlatter), with updated oe-init-build-env and TEMPLATECONF paths
• Recipe whitespace fixes -- add spaces around = in PARALLEL_MAKEINST and PACKAGE_ARCH assignments (5 files) to suppress whinlatter warnings
• LAYERSERIES_COMPAT updated from styhead to whinlatter

References

• Migration guide: https://docs.yoctoproject.org/dev/migration-guides/migration-5.3.html
• Tracking issue: Support Yocto 5.3 (whinlatter): CI and recipe migration #275

Test plan

• CI builds pass for whinlatter x86-64 and arm64
• dotnet 10.0.100, 8.0.406, 6.0.428 all build successfully
• mono 6.12.0.206 builds successfully
• Test image boots and passes testimage

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Note

Medium Risk
CI now fetches and initializes Yocto from multiple upstream repos (instead of poky), so failures are most likely due to branch/path mismatches or layer ordering; recipe changes are formatting-only but can affect parsing under newer BitBake.

Overview
Updates the project to target Yocto 5.3 whinlatter by switching LAYERSERIES_COMPAT_mono and adjusting CI to build/test against the whinlatter branch.

The GitHub Actions workflow stops cloning poky and instead clones bitbake, openembedded-core, and meta-yocto into a layers/ layout, updates TEMPLATECONF/oe-init-build-env paths accordingly, and limits the build matrix to whinlatter on x86-64 and arm64.

Separately, recipe metadata is normalized for whinlatter parsing (whitespace around =), including PARALLEL_MAKEINST in Mono include files and PACKAGE_ARCH in nuget.inc.

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