build: declare linux source input classes

[cerisier]

Summary

Make Linux source tree input classes explicit rule attributes instead of deriving them inside linux_source_tree.

The source repository now declares filegroups for full-tree files, headers, global headers, arch headers, UAPI headers, scripts headers, Kbuild files, and devicetree sources. Compact BUILD generation threads those labels through as source-tree class attrs, and object compile actions continue to consume the declared header/source groups plus direct source/generated inputs.

Measured input shape

Measured on //:kernel_arm64 from the nested e2e/ module using LinuxObjectCompile aquery output.

Before full source-tree compile inputs:

• actions: 832
• input count min/p50/p95/max: 98615 / 98615 / 98615 / 98618
• input bytes min/p50/p95/max: 1551.13 / 1551.13 / 1551.13 / 1551.35 MiB

After declared compile inputs:

• actions: 832
• input count min/p50/p95/max: 27402 / 27457 / 27615 / 27655
• input bytes min/p50/p95/max: 675.55 / 676.43 / 680.32 / 680.32 MiB

Delta:

• p50 input count: 98615 -> 27457
• p50 input bytes: 1551.13 MiB -> 676.43 MiB

[cerisier]

I thought having real filegroups is better.