Rename test support module to _SwiftFormatTestSupport.

This indicates that it should not be used by users. (In the future, it
should use `package` access-level declarations.)

Author: allevato

Package.swift

@@ -89,19 +89,19 @@ let package = Package(
       ]
     ),
     .target(
-      name: "SwiftFormatTestSupport",
+      name: "SwiftFormatWhitespaceLinter",
       dependencies: [
         "SwiftFormatCore",
-        "SwiftFormatRules",
-        "SwiftFormatConfiguration",
-        .product(name: "SwiftOperators", package: "swift-syntax"),
+        .product(name: "SwiftSyntax", package: "swift-syntax"),
       ]
     ),
     .target(
-      name: "SwiftFormatWhitespaceLinter",
+      name: "_SwiftFormatTestSupport",
       dependencies: [
         "SwiftFormatCore",
-        .product(name: "SwiftSyntax", package: "swift-syntax"),
+        "SwiftFormatRules",
+        "SwiftFormatConfiguration",
+        .product(name: "SwiftOperators", package: "swift-syntax"),
       ]
     ),
     .plugin(
@@ -158,8 +158,8 @@ let package = Package(
     .testTarget(
       name: "SwiftFormatPerformanceTests",
       dependencies: [
-        "SwiftFormatTestSupport",
         "SwiftFormatWhitespaceLinter",
+        "_SwiftFormatTestSupport",
         .product(name: "SwiftSyntax", package: "swift-syntax"),
         .product(name: "SwiftParser", package: "swift-syntax"),
       ]
@@ -171,8 +171,8 @@ let package = Package(
         "SwiftFormatCore",
         "SwiftFormatPrettyPrint",
         "SwiftFormatRules",
-        "SwiftFormatTestSupport",
         "SwiftFormatWhitespaceLinter",
+        "_SwiftFormatTestSupport",
         .product(name: "Markdown", package: "swift-markdown"),
         .product(name: "SwiftOperators", package: "swift-syntax"),
         .product(name: "SwiftParser", package: "swift-syntax"),

Sources/SwiftFormatTestSupport/Configuration+Testing.swift renamed to Sources/_SwiftFormatTestSupport/Configuration+Testing.swift

@@ -1,8 +1,8 @@
-import SwiftFormatTestSupport
 import SwiftFormatWhitespaceLinter
 import SwiftSyntax
 import SwiftParser
 import XCTest
+import _SwiftFormatTestSupport
 
 final class WhitespaceLinterPerformanceTests: DiagnosingTestCase {
   func testWhitespaceLinterPerformance() {

Sources/SwiftFormatTestSupport/DiagnosingTestCase.swift renamed to Sources/_SwiftFormatTestSupport/DiagnosingTestCase.swift

@@ -1,11 +1,11 @@
 import SwiftFormatConfiguration
 import SwiftFormatCore
 import SwiftFormatPrettyPrint
-import SwiftFormatTestSupport
 import SwiftOperators
 import SwiftSyntax
 import SwiftParser
 import XCTest
+import _SwiftFormatTestSupport
 
 class PrettyPrintTestCase: DiagnosingTestCase {
   /// Asserts that the input string, when pretty printed, is equal to the expected string.

Sources/SwiftFormatTestSupport/TestingFindingConsumer.swift renamed to Sources/_SwiftFormatTestSupport/TestingFindingConsumer.swift

@@ -1,10 +1,10 @@
 import SwiftFormatConfiguration
 import SwiftFormatCore
-import SwiftFormatTestSupport
 import SwiftFormatWhitespaceLinter
 import SwiftSyntax
 import SwiftParser
 import XCTest
+import _SwiftFormatTestSupport
 
 class WhitespaceTestCase: DiagnosingTestCase {
   override func setUp() {

Tests/SwiftFormatPerformanceTests/WhitespaceLinterPerformanceTests.swift

@@ -1,8 +1,8 @@
 import SwiftFormatCore
 import SwiftFormatRules
-import SwiftFormatTestSupport
 import SwiftParser
 import XCTest
+import _SwiftFormatTestSupport
 
 class ImportsXCTestVisitorTests: DiagnosingTestCase {
   func testDoesNotImportXCTest() throws {

Tests/SwiftFormatTests/PrettyPrint/PrettyPrintTestCase.swift

@@ -1,10 +1,10 @@
 import SwiftFormatConfiguration
 import SwiftFormatCore
-import SwiftFormatTestSupport
 import SwiftOperators
 import SwiftParser
 import SwiftSyntax
 import XCTest
+import _SwiftFormatTestSupport
 
 class LintOrFormatRuleTestCase: DiagnosingTestCase {
   /// Performs a lint using the provided linter rule on the provided input.