internal/ls: getContextNodeForNodeEntry returns nil for module-specifier literals (stock returns the enclosing import statement)

Stock's getContextNodeForNodeEntry (src/services/findAllReferences.ts:338) returns the enclosing import statement for a module-specifier string literal; tsgo returns nil. One visible effect: Go To Implementation on an import path returns a LocationLink whose target range is just the string literal instead of the whole import statement.

Minimal repro

Run go test ./internal/ls/ -run TestModuleSpecifierContextNode:

package ls

import (
	"testing"

	"github.com/microsoft/typescript-go/internal/ast"
	"github.com/microsoft/typescript-go/internal/core"
	"github.com/microsoft/typescript-go/internal/parser"
)

func TestModuleSpecifierContextNode(t *testing.T) {
	t.Parallel()
	text := "import { x } from \"./b\";\nx;\n"
	sourceFile := parser.ParseSourceFile(ast.SourceFileParseOptions{
		FileName: "/a.ts",
		Path:     "/a.ts",
	}, text, core.ScriptKindTS)

	var literal *ast.Node
	for _, stmt := range sourceFile.Statements.Nodes {
		if ast.IsImportDeclaration(stmt) {
			literal = stmt.AsImportDeclaration().ModuleSpecifier
		}
	}
	if literal == nil || literal.Kind != ast.KindStringLiteral {
		t.Fatalf("module specifier literal not found: %v", literal)
	}
	if ctx := getContextNodeForNodeEntry(literal); ctx == nil {
		t.Fatal("getContextNodeForNodeEntry(module specifier) = nil; want the enclosing import statement")
	}
}

Fails with getContextNodeForNodeEntry(module specifier) = nil on a pristine checkout (v7.0.2, 2bd066d8).

The string-literal special case diverges from stock's version (findAllReferences.ts:371): the case keys on node.Parent.Kind instead of the node itself, the FindAncestor predicate closes over the outer node instead of testing its parameter, and the outer gate's IsDeclaration(ImportDeclaration) is true in tsgo but false in stock. Same result for the other forms TryGetImportFromModuleSpecifier handles (export … from, import()/require(), …).