Add CultureInsensitiveAttribute to annotate culture-insensitive values

[meziantou]

What

Add Meziantou.Analyzer.Annotations.CultureInsensitiveAttribute. It marks the value of a property, a field, or a parameter as culture insensitive, even when its type is culture sensitive.

class Sample
{
    [CultureInsensitive]
    public static double InvariantValue => 0;
}

_ = "value: " + Sample.InvariantValue;   // no MA0075
_ = $"{Sample.InvariantValue}";          // no MA0076
_ = Sample.InvariantValue.ToString();    // no MA0011

Methods and return values are deliberately not valid targets: the attribute marks a value, not the way a method computes it, and [CultureInsensitive] on a method would be ambiguous with "this method does not depend on the culture".

Properties and fields of another assembly are annotated at the assembly level with their XML documentation id, like DoNotIgnoreAttribute does.

[assembly: CultureInsensitive("P:Sample.StringHelper.InvariantValue")]
[assembly: CultureInsensitive("F:Sample.StringHelper.InvariantField")]

A parameter is culture insensitive in both directions: reading it in the method is not reported, and MA0075/MA0076 are not reported for the arguments provided by the callers. This covers a method that formats its argument with a fixed culture, such as a wrapper around an interpolated string handler.

static void Log([CultureInsensitive] string message) { }

Log($"Value: {1.5}");  // no MA0076
Log(Format($"{1.5}")); // MA0076, the interpolated string is an argument of Format

Why

CultureInsensitiveTypeAttribute can only mark a whole type, so there was no way to opt out for a single member whose type is culture sensitive, nor for a wrapper method that formats its arguments with a fixed culture (#1316).

Notes for the reviewer

• The annotation is resolved in CultureSensitiveFormattingContext, so it applies to MA0011, MA0075, MA0076 and MA0185. For MA0185 it enables the simplification, as the annotated value counts as invariant.
• Two paths lose the symbol before reaching GetCultureSensitivity(IOperation) and are handled separately: interpolation holes and AppendFormatted calls. The instance of a ToString() call is handled as well, so invariantProperty.ToString() is not reported.
• The call-site direction of a parameter annotation deliberately affects MA0075/MA0076 only. MA0011 flags how the argument was produced, which a parameter annotation cannot change, so Log(double.Parse(text)) is still reported.
• IsInCultureInsensitiveParameterContext stops at the closest enclosing argument, so annotating a parameter never silences a value nested in another invocation. The arguments of the compiler-generated AppendFormatted calls are walked through, so a handler parameter behaves like any other parameter.
• The constructor taking a documentation id is for assembly-level annotations only: an attribute with constructor arguments is ignored when applied on a member.