Recognize a class inheriting a generic one as a child of its parent

[RomanSpector]

A class inheriting a generic one was not recognized as a child of what that generic itself inherits:

---@class Component

---@class Typed<T> : Component
---@field Value T

---@class Toggle : Typed<boolean>

---@param component Component
local function mount(component) end

---@type Toggle
local toggle

mount(toggle)   -- Cannot assign `Toggle` to parameter `Component`

A parent given with arguments is parsed into doc.type.sign, which keeps the name one level down. The inheritance walk in vm.isSubType only looked at doc.extends.name, so such a parent was skipped entirely and the chain broke at that point.

The name is now taken from the sign node as well. A test in param-type-mismatch covers the case above.

[gemini-code-assist]

Caution

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