Incorrect type on string-key fields when combined with `[string]`

### How are you using the lua-language-server?

Visual Studio Code Extension (sumneko.lua)

### Which OS are you using?

Windows

### What is the issue affecting?

Type Checking

### Expected Behaviour

we have a (generated) class like
```
---@class GlobalModSettings
---@field ["heat-visualizer-updates-per-surface-per-tick"] ModSetting
---@field ["nixie-tube-update-speed-alpha"] ModSetting
---@field ["nixie-tube-update-speed-numeric"] ModSetting
---@field [string] ModSetting<(int32)|(double)|(boolean)|(string)|(Color)>
```

which has narrower types for the known entries and a general type for the "everything else" field, but when i then use this type like
```
local x = settings.global["heat-visualizer-updates-per-surface-per-tick"]
```
`x` is given the type from the `[string]` field, rather than the one that is an exact match for that specific string

### Actual Behaviour

(this template is always off screen and i've written the whole thing in the first box...)

### Reproduction steps

(this template is always off screen and i've written the whole thing in the first box...)

### Additional Notes

_No response_

### Log File

_No response_

No repository file or test is named. Start by reproducing the annotated GlobalModSettings lookup in the Lua language server through the Visual Studio Code extension, then trace indexed-field type resolution. Done means an exact string-key field receives its narrower type instead of the broader [string] field type.

Written by the indexing model from the issue text.