[steps] Unify the default gating of steps with no if: across steps, composite scopes, and hooks

[sswrk]

Why

For a step with no if:, whether the step should run was decided in 3 separate places: BuildStep.shouldExecuteStep, the composite function scope (same rule), and the hook executor (its own rule). That bypass means composite scopes never see hook defaults, which is a blocker for adding support for composite functions in hooks.

How

A single gate now decides whether any step runs, taking a single input: a bool telling whether a step with no if: should run. Composite functions called from hooks therefore inherit the hook's rule. Steps with an explicit if: are unaffected.

Behavior-preserving refactor.

Test Plan

• Existing steps/hook tests still pass.
• Added unit coverage for the run-by-default value on shouldExecuteStep /
  isActive, and hook sibling skip/continue cases for the before/after defaults.

[linear-code]

ENG-22387

[sswrk]

• [eas-cli] Validate legacy command/path local functions referenced from workflows #4098
• [build-tools] Load legacy command/path local functions and resolve module paths #4097
• [steps] Expand legacy command/path local functions to a single build step #4096
• [eas-build-job] Accept legacy command/path custom function shape in function.yml #4095
• [eas-cli][build-tools][steps] Validate local composite functions referenced from workflow hooks; extract the shared loader into steps #4064
• [build-tools][steps] Load composite function catalogs for hook steps #4063
• [steps] Support local composite functions in hook steps #4062
• [steps] Unify the default gating of steps with no if: across steps, composite scopes, and hooks #4061 👈 (View in Graphite)
• [eas-cli] Validate local composite functions in workflow files #3931
• [build-tools] Load local composite function catalog at build runtime #3930
• [steps][4/4] Resolve composite function outputs #4015
• [steps][3/4] Interpolate composite function inputs #4014
• [steps][2/4] Expand composite function references into build steps #3929 : 1 other dependent PR (#4013 )
• [steps][1/4] Add isCompositeFunctionPath and reject local composite functions in custom builds #3956
• [eas-build-job] Add local composite function schema #3928
• main

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[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 62.29%. Comparing base (2e8cbb5) to head (3b7eed6).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
packages/steps/src/BuildWorkflow.ts	57.15%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4061      +/-   ##
==========================================
- Coverage   62.29%   62.29%   -0.00%     
==========================================
  Files         995      995              
  Lines       44888    44885       -3     
  Branches     9435     9433       -2     
==========================================
- Hits        27960    27957       -3     
  Misses      15479    15479              
  Partials     1449     1449              

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[hSATAC]

LGTM.

[github-actions]

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