Added correct detection of conformance scopes when inside a public extension

[bok-]

📒 Description

Vexil 3's @FlagContainer macro generates conformances to FlagContainer and Equatable. At the moment we were only looking at the attached declaration to see if we needed to generate public conformances, but if we're inside a public extension we wouldn't know. eg:

public extension SomeContainer {
    @FlagContainer
    struct SomeFlags {}
}

🔍 Detailed Design

This PR uses SwiftSyntax 6's lexical context to look at the declaration's parent and see if its a public extension.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud