Tab character incorrectly assumed to be composed of 8 characters

### Your environment
Output of `haskell-language-server --probe-tools` or `haskell-language-server-wrapper --probe-tools`:

```sh
haskell-language-server version: 1.0.0.0 (GHC: 8.10.4) (PATH: [MYHOME]/.ghcup/bin/haskell-language-server-wrapper-1.0.0) (GIT hash: 4cd1cf934638881e52b3eba9f70157a4b799c0e9)
Tool versions found on the $PATH
cabal: 3.4.0.0
stack: 2.7.1
ghc: 8.6.5

```
Which OS do you use: Ubuntu

Which lsp-client do you use: Vim with Coc

Describe your project (alternative: link to the project): stack-project

Contents of `hie.yaml`:
```yaml
cradle:
stack:
component: "name-of-project:lib"
```

### Steps to reproduce

Type the following code
```haskell
module Test where

main :: IO ()
main = do
putStr "hello" -- there is a tab-character (\t) in front of putStr
```
And request information about `putStr`
### Expected behaviour

I should get a pop-up with type information and a short description.

### Actual behaviour

I get a pop-up about `IO` instead.
If I put my cursor further ahead, over the string "hello", I do get information about `putStr`. It seems HLS treats a tab as 8 separate characters. Setting a tab-size of 8 does not help, since it is still one character.
### Include debug information
Paste the logs from the lsp-client, e.g. for [VS Code](https://github.com/haskell/vscode-haskell#troubleshooting)

LSP logs:

The first part is when the cursor is on `putStr` and gives information about `IO`, the second part is when the cursor is on the last part of "hello" and gives information about `putStr`

File: [hls-output.txt](https://github.com/haskell/haskell-language-server/files/6727553/hls-output.txt)

Gist: [hls-output.txt gist](https://gist.github.com/LiraOnGithub/42d94188632e3343a83f9e98a24bd149)

Please let me know if you need more of the output.