No Protection on enum values as function input

Nobody has claimed this yet.

Currently with code like the following:

```
---@enum TestEnum
TestEnum = {
ONE = "ONE",
TWO = "TWO",
THREE = "THREE",
}

---@param test_enum TestEnum
local function test(test_enum)
print(test_enum)
end

test(TestEnum.ONE) --- CORRECT: No error
test("ONE") --- CORRECT: No error
test(TestEnum.FOUR) --- INCORRECT: No error
test("FOUR") --- CORRECT: Error
```

There is no intellisense error for `test(TestEnum.FOUR)` like there is for `test("FOUR")`

It would be nice to get an error if you are trying to use a non-existing enum value (I have run into problems relating to this 😞) similarly if you are trying to use a string literal which doesn't match the enum.

I think this might be related to a wider issue where inputs to functions can be of type unknown even with the no-unknown setting.

Use the provided enum and function example as the reproduction, comparing diagnostics for TestEnum.FOUR and "FOUR". Trace the language server's enum and function-argument type checking, then add coverage for both calls; done when the invalid enum member is diagnosed consistently with the invalid string literal.

Written by the indexing model from the issue text.