Add fixer for "dotnet format" (#3879)

The .NET ecosystem has an official tool for formatting its files: `dotnet format`
This adds support for that tool to ALE.

doc/ale-cs.txt

@@ -90,6 +90,39 @@ g:ale_cs_csc_assemblies                               *g:ale_cs_csc_assemblies*
     \]
 <
 
+===============================================================================
+dotnet-format                                            *ale-cs-dotnet-format*
+
+Installation
+-------------------------------------------------------------------------------
+
+Installing .NET SDK should probably ensure that `dotnet` is in your `$PATH`.
+For .NET 6 the `dotnet format` tool is already included in the .NET SDK. For
+.NET 5 or below you will have to manually install it using the instructions
+from listed in this repository: https://github.com/dotnet/format
+
+
+Options
+-------------------------------------------------------------------------------
+
+g:ale_cs_dotnet_format_executable           *g:ale_cs_dotnet_format_executable*
+                                            *b:ale_cs_dotnet_format_executable*
+  Type: |String|
+  Default: `'dotnet'`
+
+  This variable can be set to specify an absolute path to the
+  `dotnet` executable (or to specify an alternate executable).
+
+
+g:ale_cs_dotnet_format_options                 *g:ale_cs_dotnet_format_options*
+                                               *b:ale_cs_dotnet_format_options*
+  Type: |String|
+  Default: `''`
+
+  This variable can be set to pass additional options to the `dotnet format`
+  fixer.
+
+
 ===============================================================================
 mcs                                                                *ale-cs-mcs*
 

doc/ale-supported-languages-and-tools.txt

@@ -66,6 +66,7 @@ Notes:
   * `uncrustify`
 * C#
   * `csc`!!
+  * `dotnet-format`
   * `mcs`
   * `mcsc`!!
   * `uncrustify`

doc/ale.txt

@@ -2681,6 +2681,7 @@ documented in additional help files.
     uncrustify............................|ale-cpp-uncrustify|
   c#......................................|ale-cs-options|
     csc...................................|ale-cs-csc|
+    dotnet-format.........................|ale-cs-dotnet-format|
     mcs...................................|ale-cs-mcs|
     mcsc..................................|ale-cs-mcsc|
     uncrustify............................|ale-cs-uncrustify|