MA0003: don't require naming extension receivers and self-named arguments - #1361

Two cases where MA0003 asked for a named argument that could not be written, or that would not have improved readability.

[RequireNamedArgument] on an extension-method receiver

The attribute is now ignored on the this parameter of an extension method.

Before this change the behavior depended on the call syntax: value.Foo() has no argument to name at all, so nothing was reported, while Ext.Foo(value) mapped the argument to the this parameter and reported a diagnostic. Naming the receiver is never the readability win the attribute is meant to ask for, so the parameter is now skipped in both forms.

The check also covers C# 14 extension(...) blocks: their synthesized static method exposes the receiver as an extension-method parameter at ordinal 0, and the attribute written on the extension(...) clause does flow to it — I verified both with a Roslyn probe, and the corresponding tests fail when the guard is removed.

Arguments already carrying the name of the parameter

Foo(sample) for a parameter named sample is no longer reported — naming it would only repeat the name:

var sample = 0;
Foo(sample);  // no diagnostic

void Foo([RequireNamedArgument] int sample) { }

Details:

• Covers locals, parameters, properties, and fields; the comparison ignores the case.
• For fields, the _ and s_ prefixes are removed before comparing, so Foo(_sample) and Foo(s_sample) also match a parameter named sample.
• The prefixes are stripped for fields only. A local named _sample is still reported, since the prefix is not a convention for locals and silencing it would hide real cases.
• The raw name is compared before stripping, so a field _sample still matches a parameter actually named _sample.
• The new MA0003.ignore_arguments_matching_parameter_name option (default true) turns the behavior off.

In practice this only affects the [RequireNamedArgument] path: the general MA0003 rule reports literals, which have no name. The check is placed on the shared path anyway so it applies to the rule as a whole.

Notes for the reviewer

• The general MA0003 rule is deliberately left alone for extension receivers: Ext.Foo(null) still reports as before. Only the attribute path changed, matching what was asked for.
• The config lookup for the new option only runs once the names actually match, so it costs nothing on the common path.
• While restructuring, the two GetOperation calls previously made for every argument were folded into one.
• No file under src/Meziantou.Analyzer.Annotations changed, so no package version bump; the attribute's new behavior is documented on the MA0003 page the annotations README already links to.

Testing

• 13 new tests in NamedParameterAnalyzerTests (the extension(...) block one guarded by #if CSHARP14_OR_GREATER), passing on all five Roslyn versions.
• Full suite: 18972 tests, 0 failures.
• dotnet run --project src/DocumentationGenerator run until it reported no further changes.