Add the generic struct support

[janartodesk]

Add support for extracting translations from generic struct fields and methods.

The struct field extraction logic is aligned with the function call's extraction logic, and the generic struct handling logic is added.

Redesign util.ObjectToKey() helper to support the generic struct use-case.

The funcCallExtractor targets *ast.CallExpr, whereas the definitionExtractorRunner *ast.FuncDecl AST nodes. Using the util.ObjectToKey() helper on these two targets returns inconsistent object keys for the same logical AST node.

Given a generic struct

type Struct[T any] struct{}

func (Struct[T]) Method(localize.Singular) {}

used as

(Struct[string]{}).Method("To be translated")

resolves to the following object key specification

• github.com/vorlif/testdata/debug.func (github.com/vorlif/testdata/debug.GenericStruct[string]).Method(string) for the funcCallExtractor, but
• github.com/vorlif/testdata/debug.func (github.com/vorlif/testdata/debug.GenericStruct[T]).Method(string) for the definitionExtractorRunner

resulting in translation targets not being mappable between different invocations, and omitted from the output.

The change in design introduces a simplified object keying pattern, which relies on symbol names being unique within a package context to generate globally unique keys, allowing more control over the key's format.

The *ast.CallExpr and *ast.FuncDecl type name formatting discrepancy is solved by reformatting the type name string. This simplistic approach is used due to the *types.Signature type's limited API which doesn't expose higher granularity typing information.