7bd7b6dfadc44a6e47f4d1851d63c76276f1a94c  Add CString::legacyCStringPointer() and adopt it at every utf8().data() call site

Classified as not security-relevant.
Triage note: Mechanical API rename across the tree: CString::utf8().data() calls migrated to a new legacyCStringPointer() escape-hatch accessor (plus a few SAFE_PRINTF swaps). Encoding-type migration with no behavior change or bug fixed.
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), security_assert (+3.0), msg_noise (-2.5), area:Source/JavaScriptCore/bytecode (+2.5), large_churn (-2.0)