Bootstrap: dedupe spine requires + VmObjectDebugType unit (#17412)

[PurHur]

Summary

• Remove 12 duplicate require_once lines in compiler_lib_spine_smoke/main.php (parallel spine PR merge fallout — clamp, date_set, intl constants).
• Add ext/standard/VmObjectDebugType.php to the spine before get_debug_type.php (dependency was in inventory but not required).
• Sync M2 footnotes to 4284/4284 and refresh docs/bootstrap-inventory.md.

Closes #17412
Closes #17446

Root cause

Two racing spine-sync PRs duplicated the same require_once entries; VmObjectDebugType.php landed on the vm.php path via get_debug_type.php without its own spine line.

Verification

php script/check-selfhost-spine-count-sync.php
# check-selfhost-spine-count-sync: OK (spine 4284/4284 from compiler_lib_spine_smoke)

php script/check-selfhost-spine-coverage-sync.php
# check-selfhost-spine-coverage-sync: OK (spine covers all 4284 inventory files)

php script/check-selfhost-spine-deferred-sync.php
# check-selfhost-spine-deferred-sync: OK (0 deferred: (none); spine 4284/4284)

php script/bootstrap-inventory.php --check
# OK 4284/4284

vendor/bin/phpunit --filter testCompilerLibSpineSmokeBundleUnitCountAndKeyUnits test/unit/BootstrapSelfhostBundleTest.php
# OK (1 test, 478 assertions)

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