[Feature Request] Diagnostic for using wrong require separator

[jllv]

The setting completion.requireSeparator allows the user to define a certain character to use as the separator when require-ing a file. It would be nice to have a diagnostic that warns the user if he violates this setting.

Example

"Lua.completion.requireSeparator": {
                    "default": "/"
}

local strings = require("helpers.strings")
                               ^^^  --Warning: Wrong separator