Let resource_set callbacks opt into the inputs' total size

[rdesgroppes]

Description

Starlark resource_set callbacks declaring an inputs_bytes parameter (or **kwargs) now also receive the total size in bytes of the action's expanded inputs, as that keyword argument. Other callbacks keep being called with exactly (os, inputs_size).

Local runners pass the size lazily to the new Spawn.getLocalResources(InputsBytes), as computed by SpawnExecutionContext.getInputsBytes() from the input mapping and metadata they already hold. It's therefore only summed for declarations asking for it, and without downloading inputs. ResourceSetOrBuilder gains needsInputsBytes() and a 3-argument buildResourceSet, both defaulting to the existing behavior, so native estimators are unaffected. Callers without input metadata at hand, such as tests, pass InputsBytes.UNKNOWN explicitly.

Motivation

Link steps' memory scales with the bytes they link, which the input count misses for the links most at risk of OOM kills, as measured in #31827.

Fixes #31827.

Build API Changes

Does this PR affect the Build API? (e.g. Starlark API, providers, command-line flags, native rules)
=> Yes
If yes, please answer the following:

1. Has this been discussed in a design doc or issue? (Please link it)
   => Pass the total size in bytes of an action's inputs to Starlark resource_set callbacks #31827.
2. Is the change backward compatible?
   => Backward compatible: callbacks only receive inputs_bytes when declaring it (or **kwargs).
3. If it's a breaking change, what is the migration plan?
   => Not a breaking change.

Checklist

• I have added tests for the new use cases (if any).
• I have updated the documentation (if applicable).

Release Notes

RELNOTES[NEW]: resource_set callbacks declaring an inputs_bytes parameter receive the total size in bytes of the action's inputs.