Rename helper function for readability

Clarifies the function name so that it clearly states that only top level nodes are returned, as well as improving the grammar at the call site.

Author: anferbui

Tests/SwiftDocCTests/Indexing/ExternalRenderNodeTests.swift

@@ -269,15 +269,15 @@ class ExternalRenderNodeTests: XCTestCase {
         XCTAssertEqual(renderIndex.interfaceLanguages[SourceLanguage.objectiveC.id]?.count(where: \.isExternal), 0)
 
 
-        func externalNodes(by language: SourceLanguage) -> [RenderIndex.Node]? {
+        func externalTopLevelNodes(for language: SourceLanguage) -> [RenderIndex.Node]? {
             renderIndex.interfaceLanguages[language.id]?.first?.children?.filter(\.isExternal)
         }
 
         // Verify that the curated external links are part of the index.
-        let swiftExternalNodes = try XCTUnwrap(externalNodes(by: .swift))
+        let swiftExternalNodes = try XCTUnwrap(externalTopLevelNodes(for: .swift))
         XCTAssertEqual(swiftExternalNodes.count, 2)
 
-        let objcExternalNodes = try XCTUnwrap(externalNodes(by: .objectiveC))
+        let objcExternalNodes = try XCTUnwrap(externalTopLevelNodes(for: .objectiveC))
         XCTAssertEqual(objcExternalNodes.count, 2)
 
         let swiftArticleExternalNode = try XCTUnwrap(swiftExternalNodes.first(where: { $0.path == "/path/to/external/swiftarticle" }))
@@ -358,13 +358,13 @@ class ExternalRenderNodeTests: XCTestCase {
         XCTAssertEqual(renderIndex.interfaceLanguages[SourceLanguage.swift.id]?.count(where: \.isExternal), 0)
         XCTAssertEqual(renderIndex.interfaceLanguages[SourceLanguage.objectiveC.id]?.count(where: \.isExternal), 0)
 
-        func externalNodes(by language: SourceLanguage) -> [RenderIndex.Node]? {
+        func externalTopLevelNodes(for language: SourceLanguage) -> [RenderIndex.Node]? {
             renderIndex.interfaceLanguages[language.id]?.first?.children?.filter(\.isExternal)
         }
 
         // Verify that the curated external links are part of the index.
-        let swiftExternalNodes = try XCTUnwrap(externalNodes(by: .swift))
-        let objcExternalNodes = try XCTUnwrap(externalNodes(by: .objectiveC))
+        let swiftExternalNodes = try XCTUnwrap(externalTopLevelNodes(for: .swift))
+        let objcExternalNodes = try XCTUnwrap(externalTopLevelNodes(for: .objectiveC))
 
         XCTAssertEqual(swiftExternalNodes.count, 1)
         XCTAssertEqual(objcExternalNodes.count, 1)