Make the retainFeatureCheckIfConfigs version of removingInactive compiler SPI

I'm not sure we have any clients for this particular option outside of
the compiler, so for now, limit it to the compiler. We can expose it later
if we'd like.

Author: DougGregor

Sources/SwiftIfConfig/ActiveSyntaxRewriter.swift

@@ -14,6 +14,24 @@ import SwiftDiagnostics
 import SwiftSyntax
 
 extension SyntaxProtocol {
+  /// Produce a copy of this syntax node that removes all syntax regions that
+  /// are inactive according to the given build configuration, leaving only
+  /// the code that is active within that build configuration.
+  ///
+  /// If there are errors in the conditions of any configuration
+  /// clauses, e.g., `#if FOO > 10`, then the condition will be
+  /// considered to have failed and the clauses's elements will be
+  /// removed.
+  /// - Parameters:
+  ///   - configuration: the configuration to apply.
+  /// - Returns: the syntax node with all inactive regions removed, along with
+  ///   an array containing any diagnostics produced along the way.
+  public func removingInactive(
+    in configuration: some BuildConfiguration
+  ) -> (result: Syntax, diagnostics: [Diagnostic]) {
+    return removingInactive(in: configuration, retainFeatureCheckIfConfigs: false)
+  }
+
   /// Produce a copy of this syntax node that removes all syntax regions that
   /// are inactive according to the given build configuration, leaving only
   /// the code that is active within that build configuration.
@@ -29,9 +47,10 @@ extension SyntaxProtocol {
   ///     feature checks.
   /// - Returns: the syntax node with all inactive regions removed, along with
   ///   an array containing any diagnostics produced along the way.
+  @_spi(Compiler)
   public func removingInactive(
     in configuration: some BuildConfiguration,
-    retainFeatureCheckIfConfigs: Bool = false
+    retainFeatureCheckIfConfigs: Bool
   ) -> (result: Syntax, diagnostics: [Diagnostic]) {
     // First pass: Find all of the active clauses for the #ifs we need to
     // visit, along with any diagnostics produced along the way. This process