getValue was the last camelCase half of the value accessor pair; its
partner setValue was renamed in c4c0b10 and shipped in 3.3.0. Follow
that commit's shape: rename outright through the internal machinery
(LiteralABC, Literal, Argument, Operator, ParameterProxy,
ParameterAdapter) and all internal call sites, and add a forwarding
@deprecated shim on the user-facing class.

Unlike setValue, getValue is reachable on the Operator side of the
hierarchy too, so the shim goes on Literal as well as on Parameter.
Parameter's overrides Literal's, so Parameter users get a message
naming Parameter.get_value and everyone else gets one naming
Literal.get_value. Argument, Operator, Equation, ParameterProxy and
ParameterAdapter all keep accepting getValue.

This unblocks the structure and sas subpackage renames, which could not
rename their getValue overrides while core still dispatched on the old
name.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>