Enable upcoming feature 'MemberImportVisibility' and fix issues it reveals (#1020)

This enables the `MemberImportVisibility` upcoming Swift feature
described in [SE-0444: Member import
visibility](https://github.com/swiftlang/swift-evolution/blob/main/proposals/0444-member-import-visibility.md),
then fixes the new issues that enabling it reveals.

### Checklist:

- [x] Code and documentation should follow the style of the [Style
Guide](https://github.com/apple/swift-testing/blob/main/Documentation/StyleGuide.md).
- [x] If public symbols are renamed or modified, DocC references should
be updated.

Author: stmontgomery

Package.swift

@@ -202,6 +202,8 @@ extension Array where Element == PackageDescription.SwiftSetting {
       .enableExperimentalFeature("AccessLevelOnImport"),
       .enableUpcomingFeature("InternalImportsByDefault"),
 
+      .enableUpcomingFeature("MemberImportVisibility"),
+
       // This setting is enabled in the package, but not in the toolchain build
       // (via CMake). Enabling it is dependent on acceptance of the @section
       // proposal via Swift Evolution.

Sources/Testing/ABI/ABI.Record+Streaming.swift

@@ -9,6 +9,8 @@
 //
 
 #if canImport(Foundation) && (!SWT_NO_FILE_IO || !SWT_NO_ABI_ENTRY_POINT)
+private import Foundation
+
 extension ABI.Version {
   /// Post-process encoded JSON and write it to a file.
   ///

Sources/TestingMacros/ConditionMacro.swift

@@ -9,6 +9,7 @@
 //
 
 public import SwiftSyntax
+import SwiftSyntaxBuilder
 public import SwiftSyntaxMacros
 
 #if !hasFeature(SymbolLinkageMarkers) && SWT_NO_LEGACY_TEST_DISCOVERY

Sources/TestingMacros/PragmaMacro.swift

@@ -8,6 +8,8 @@
 // See https://swift.org/CONTRIBUTORS.txt for Swift project authors
 //
 
+import SwiftDiagnostics
+import SwiftParser
 public import SwiftSyntax
 public import SwiftSyntaxMacros
 

Sources/TestingMacros/SuiteDeclarationMacro.swift

@@ -8,7 +8,9 @@
 // See https://swift.org/CONTRIBUTORS.txt for Swift project authors
 //
 
+import SwiftDiagnostics
 public import SwiftSyntax
+import SwiftSyntaxBuilder
 public import SwiftSyntaxMacros
 
 #if !hasFeature(SymbolLinkageMarkers) && SWT_NO_LEGACY_TEST_DISCOVERY

Sources/TestingMacros/Support/Additions/MacroExpansionContextAdditions.swift

@@ -9,6 +9,7 @@
 //
 
 import SwiftSyntax
+import SwiftSyntaxBuilder
 import SwiftSyntaxMacros
 import SwiftDiagnostics
 

Sources/TestingMacros/Support/Additions/TokenSyntaxAdditions.swift

@@ -8,6 +8,7 @@
 // See https://swift.org/CONTRIBUTORS.txt for Swift project authors
 //
 
+import SwiftParser
 import SwiftSyntax
 
 extension TokenSyntax {

Sources/TestingMacros/Support/Argument.swift

@@ -9,6 +9,7 @@
 //
 
 import SwiftSyntax
+import SwiftSyntaxBuilder
 
 /// A type describing an argument to a function, closure, etc.
 ///

Sources/TestingMacros/Support/AttributeDiscovery.swift

@@ -9,6 +9,7 @@
 //
 
 import SwiftSyntax
+import SwiftSyntaxBuilder
 import SwiftSyntaxMacros
 
 /// A syntax rewriter that removes leading `Self.` tokens from member access

Sources/TestingMacros/Support/AvailabilityGuards.swift

@@ -9,6 +9,7 @@
 //
 
 import SwiftSyntax
+import SwiftSyntaxBuilder
 import SwiftSyntaxMacros
 
 /// A structure describing a single platform/version pair from an `@available()`