file_icons: Add separate icon keys for .NET solution and project files (#24851)

Add separate icon keys for .NET solution and project files.

Release Notes:

- Icon themes: Added the ability to change file icons for Visual Studio
project files:
  - Solution files (`.sln`)
  - Solution User Options files (`.suo`)
  - C# Project files (`.csproj`)
  - F# Project files (`.fsproj`)
  - Visual Basic Project files (`.vbproj`)

---------

Co-authored-by: Marshall Bowers <git@maxdeviant.com>

assets/icons/file_icons/file_types.json

@@ -36,6 +36,7 @@
     "cpp": "cpp",
     "cr": "crystal",
     "cs": "csharp",
+    "csproj": "csproj",
     "css": "css",
     "csv": "storage",
     "cts": "typescript",
@@ -72,6 +73,7 @@
     "fp7": "storage",
     "frm": "storage",
     "fs": "fsharp",
+    "fsproj": "fsproj",
     "gdb": "storage",
     "gif": "image",
     "gitattributes": "vcs",
@@ -196,6 +198,7 @@
     "scss": "sass",
     "sdf": "storage",
     "sh": "terminal",
+    "sln": "vs_sln",
     "sol": "solidity",
     "sql": "storage",
     "sqlite": "storage",
@@ -210,6 +213,7 @@
     "stylelintrc.mjs": "stylelint",
     "stylelintrc.yaml": "stylelint",
     "stylelintrc.yml": "stylelint",
+    "suo": "vs_suo",
     "svelte": "svelte",
     "svg": "image",
     "swift": "swift",
@@ -224,6 +228,7 @@
     "ttf": "font",
     "txt": "document",
     "v": "v",
+    "vbproj": "vbproj",
     "vsh": "v",
     "vue": "vue",
     "vv": "v",