7b265b345c261337cd1148ee074baf3167a9e714  [GTK][WPE] `steps()` and `linear()` animations can be accelerated

Classified as not security-relevant.
Triage note: TextureMapperAnimation refactor splitting m_timingFunction from m_defaultTimingFunctionForKeyframes and adding timingFunctionForKeyframe(), plus a USE(CA) guard around steps/linear acceleration checks. Animation timing-function selection correctness, not a security bug.
This commit was flagged by the signal scorer and reviewed by AI (not a human). It is listed only so the triage is auditable; there is no root-cause analysis because this is not a vulnerability fix.

Structural signals: smartptr_member_added (+6.47), null_guard (+2.59)