`hls-rename-plugin` can’t rename import aliases

## Is your enhancement request related to a problem? Please describe.

Sometimes I find it difficult to organize my imports, because `hls-rename-plugin` doesn’t support renaming import aliases.

For example, consider the following code:

```haskell
import qualified Data.List as L

betterTail = L.drop 1
```

Now, suppose I want to rename `L` because I want to import `Control.Lens as L` and refer to `Data.List` as `List` instead.

`hls-rename-plugin` can’t do this yet. Specifically:

- If I place my cursor on `L` in `as L`, the plugin says “No symbol to rename at given location.”
- If I place my cursor on `L` in `L.drop` and attempt to rename `L` to `List`, I get “Renaming of an imported name is unsupported.”

## Describe the solution you'd like

I want to be able to place my cursor on an import alias (whether in an import statement or in a qualified name), and rename the alias.

For example, I should be able go to either `L` below, rename it to `List`, and have all occurrences of `L` changed correctly:

```haskell
-- Before: ----------------------------

import qualified Data.List as L

betterTail = L.drop 1

-- After: -----------------------------

import qualified Data.List as List

betterTail = List.drop 1
```

### Bonus

I also want to be able to rename the following aliases *separately*:

```haskell
-- Before: ----------------------------

import Control.Monad as M
import Data.Maybe as M

isSomething = M.isJust -- from Maybe
discard = M.void -- from Monad

-- After: -----------------------------

import Control.Monad as Monad
import Data.Maybe as Maybe

isSomething = Maybe.isJust -- from Maybe
discard = Monad.void -- from Monad
```

## Describe alternatives you've considered

I tried search-and-replace, but it always felt less convenient and more error prone.

For example, if I have two aliases named `L` and `URL`, doing search-and-replace to rename `L` to `List` might also turn `URL` to `URList`.

## Additional context

I think there’s none.