Complete the Classic Era 1.15.9 C_AddOns fix (stacked on #320)

[Pimptasty]

Please merge #320 first — this PR is stacked on top of it

This branch is built directly on @umuppetu's #320 (ffbb27a), not on master. Until #320 is merged, the diff shown here includes their two commits as well as mine. Once #320 lands, this PR's diff reduces to just the two commits below and applies cleanly.

Merge order: #320, then this. If you'd rather have it as a single PR, say so and I'll rebase onto master and fold #320's changes in with credit.

What #320 already fixes

Classic Era 1.15.9 completed the C_AddOns migration Retail did in 11.0 and removed the AddOn API globals. ItemRack.lua's first executable statement called GetAddOnMetadata, so the file aborted at load and nothing initialized — the reported symptom in #319. #320 correctly guards that, plus the ItemRackButtons.lua uses.

What this adds

Lua locals don't cross file boundaries, and #320's ItemRack.lua alias only covers GetAddOnMetadata. Three call sites still resolve to the removed globals:

File	Line	Call	Function
ItemRack/ItemRack.lua	1946	EnableAddOn	ItemRack.ToggleOptions
ItemRack/ItemRack.lua	1947	LoadAddOn	ItemRack.ToggleOptions
ItemRack/ItemRackEvents.lua	280	LoadAddOn	ItemRack.ToggleEvents

Both paths load the LoD ItemRackOptions, so with #320 alone the addon loads but opening the options panel or toggling events still throws attempt to call a nil value.

This uses the same guarded pattern as #320, so TBC/Wrath/Cata — which still only have the globals — resolve to them unchanged:

local LoadAddOn = (C_AddOns and C_AddOns.LoadAddOn) or LoadAddOn

I checked ItemRackOptions/ separately; it has no affected call sites.

Second commit: Interface-Vanilla bump

Classic Era is on 1.15.9 / interface 11509, while both .toc files still declare ## Interface-Vanilla: 11505, so the addon flags as out of date. Only the Vanilla line is changed in each; TBC/Wrath/Cata values are untouched. Drop this commit if you'd rather handle toc bumps in your own release commits.

Verification

• All four Lua files compile clean under luac -p.
• Verified against a live 1.15.9 (build 68940) Classic Era client that C_AddOns.GetAddOnMetadata, .LoadAddOn and .EnableAddOn all exist and are in active use by other addons on that client.
• Confirmed by inspection that every one of the six affected call sites across the three files now has a matching file-level alias in scope.
• I have not yet exercised the options-panel and toggle-events paths in-game post-patch; the fix is a direct like-for-like substitution, but calling that out rather than claiming more than I've run.

Refs #319. Does not touch the binding/macro changes proposed in #318.

🤖 Generated with Claude Code