feat: Added ConfigFile to simplify AnalyzerConfigFile creation.

[HavenDV]

I recently got acquainted with your package and for me creating a configuration file was problematic until I found an example. I think this can simplify the entry threshold because it adds a specific Add method that will be used intuitively.

[sharwell]

I'm a bit hesitant to add this here in the current form. Note that you can achieve the same outcome by defining the Add method as an extension method in your own project.

Here are issues I'd like to see addressed in a general API:

1. Allow adding /.editorconfig or /.globalconfig without specifying the file name directly.
2. Avoid having the new Add method apply to ProjectState.Sources, ProjectState.AdditionalFiles, or ProjectState.GeneratedSources.
3. Avoid the need to type new Dictionary<string, Dictionary<string, string>> or new Dictionary<string, string>, similar to how we avoid the need to type new ProjectState(projectName, language, $"/{projectName}/Test", extension) when adding items to SolutionState.AdditionalProjects.

[sharwell]

See notes in review

[HavenDV]

Thank you. Tried to take into account your comments.
The only downside I don't like about the new implementation is the duplication of the section key here if you need to add multiple values to the same section.

var actual = new EditorConfigFile
{
    ["root"] = "true",
    ["*", "key"] = "{|Literal:value|}",
}.ToString();

[sharwell]

The only downside I don't like about the new implementation is the duplication of the section key here if you need to add multiple values to the same section.

I did notice this. I believe you could resolve this by making root be a constructor parameter:

var actual = new EditorConfigFile(root: true)
{
  ["*"] =
  {
    "key = {|Literal:value|}",
  },
}.ToString();

or:

var actual = new EditorConfigFile(root: true)
{
  ["*"] =
  {
    { "key", "{|Literal:value|}" },
  },
}.ToString();

[HavenDV]

Perhaps I do not understand something, but how to specify global values other than root, which can be anything?

Will the values for the * section be available via AnalyzerConfigOptionsProvider.GlobalOptions?