pfUI's Lua hooksecurefunc lived in pfUI.env and shadowed ClassicAPI's C
global for all pfUI code. Replace it with a thin pfUI.hooksecurefunc shim
that keeps the missing-target no-op our call sites rely on (ClassicAPI
errors on a nil target) and delegates the actual hook to _G.hooksecurefunc.
Migrated all 70 internal call sites (modules/libs/skins) to
pfUI.hooksecurefunc; bare hooksecurefunc now resolves to ClassicAPI's C
version everywhere. Dropped the unused prepend path and the orphaned
pfUI.hooks table.
Add tooltip library, based on the sellvalue item hooks,
in order to obtain extended gametooltip data, that can be used
to query the current GameTooltip for ItemLink and ItemID.
Brues