VS Code extension does not handle module case (in)sensitivity correctly

**Bicep version**
0.18.4

**Describe the bug**
Noticed following issue in the VS Code Extension running on Windows after renaming the module file from `resourcegroup.bicep` to `resourceGroup.bicep`:

One would expect to see red lines to indicate the filename being incorrect. However as Windows is case insensitive, it shows no error and deployments still work. Running on Linux (typically ubuntu-latest as build agent), you will get an error that says it can't find the file (due to case sensitivity)

```
Error BCP091: An error occurred reading file. Could not find file '/home/vsts/work/1/s/modules/resources/resourcegroup.bicep'.
```

**To Reproduce**
Steps to reproduce the behavior:

- Create a bicep deployment with a module
- Rename the file (on Windows) by changing capitalization
- Try to deploy on Windows
- Try to deploy on Linux

Start by reproducing the module rename scenario in the VS Code extension on Windows and Linux, using the referenced module file and deployment steps. Trace how the extension resolves module paths and reports diagnostics; done means a capitalization mismatch is identified consistently before deployment.

Written by the indexing model from the issue text.