feat(lang/fsharp): add F# support to omnisharp extra (#6538)

## Description
Extend the existing C#/VB setup to support F# development with
formatting, LSP, and debugging integration.

- Extend recommended filetypes and roots to include F#
- Ensure Treesitter installs the `fsharp` parser
- Add Fantomas formatter in none-ls and Conform
- Ensure Mason installs fsautocomplete and fantomas
- Extend DAP configurations to include `fsharp`

⚠️ For debugging/neotest to work, this PR should be merged together with
[#6540](https://github.com/LazyVim/LazyVim/pull/6540),
which switches Omnisharp extras from `neotest-dotnet` to
`neotest-vstest`.

## Related Issue(s)

N/A

## Screenshots

### Without PR

Sample code:
<img width="1485" height="934" alt="2025-09-27-224704_hyprshot"
src="https://github.com/user-attachments/assets/40993ae2-c7eb-458a-bca9-6e77a1fad323"
/>

### With PR

`:ConformInfo`
<img width="1280" height="573" alt="image"
src="https://github.com/user-attachments/assets/b417fce7-8eb5-4ccc-8bd4-c554060bf9a0"
/>

`:NullLsInfo`
<img width="732" height="544" alt="image"
src="https://github.com/user-attachments/assets/5275e16b-353f-4776-b130-09ec27fde90b"
/>

Sample code before formatting:
<img width="1953" height="1228" alt="2025-09-27-224729_hyprshot"
src="https://github.com/user-attachments/assets/870b17c7-2473-4151-9ccc-23b70d9fbc42"
/>

Sample code after formatting (using Fantomas formatter):
<img width="1930" height="1216" alt="2025-09-27-224752_hyprshot"
src="https://github.com/user-attachments/assets/3b589c2e-b7b2-4fbf-bef7-0aabda586536"
/>

DAP/Neotest debugging the sample code: 
<img width="2548" height="1461" alt="image"
src="https://github.com/user-attachments/assets/b70a9498-041e-48c8-8e7c-78a828d0e17d"
/>



## Attachments
[Sample Project ZIP
Archive](https://github.com/user-attachments/files/22576868/FsSample.zip)

```
sudo pacman -S --needed curl unzip dotnet-sdk # or whatever package manger is on system
curl -O -L "https://github.com/user-attachments/files/22576868/FsSample.zip"
unzip FsSample.zip
cd FsSample
dotnet build  # restoring/building fixes LSP errors 
```     

## Checklist

- [X] I've read the
[CONTRIBUTING](https://github.com/LazyVim/LazyVim/blob/main/CONTRIBUTING.md)
guidelines.

Co-authored-by: Christoph Schmidpeter <christoph.schmidpeter@gmail.com>

lua/lazyvim/plugins/extras/lang/omnisharp.lua

@@ -1,15 +1,15 @@
 return {
   recommended = function()
     return LazyVim.extras.wants({
-      ft = { "cs", "vb" },
-      root = { "*.sln", "*.csproj", "omnisharp.json", "function.json" },
+      ft = { "cs", "vb", "fsharp" },
+      root = { "*.sln", "*.csproj", "*.fsproj", "omnisharp.json", "function.json", "paket.dependencies", "paket.lock" },
     })
   end,
 
   { "Hoffs/omnisharp-extended-lsp.nvim", lazy = true },
   {
     "nvim-treesitter/nvim-treesitter",
-    opts = { ensure_installed = { "c_sharp" } },
+    opts = { ensure_installed = { "c_sharp", "fsharp" } },
   },
   {
     "nvimtools/none-ls.nvim",
@@ -18,6 +18,7 @@ return {
       local nls = require("null-ls")
       opts.sources = opts.sources or {}
       table.insert(opts.sources, nls.builtins.formatting.csharpier)
+      table.insert(opts.sources, nls.builtins.formatting.fantomas)
     end,
   },
   {
@@ -26,12 +27,13 @@ return {
     opts = {
       formatters_by_ft = {
         cs = { "csharpier" },
+        fsharp = { "fantomas" },
       },
     },
   },
   {
     "mason-org/mason.nvim",
-    opts = { ensure_installed = { "csharpier", "netcoredbg" } },
+    opts = { ensure_installed = { "csharpier", "netcoredbg", "fsautocomplete", "fantomas" } },
   },
   {
     "neovim/nvim-lspconfig",