[ios, macos] Look more widely for IBDesignablesAgent

The IBDesignablesAgent helper process has been renamed for each platform as of Xcode 10, so cast a wider net when trying to detect it.

platform/darwin/src/NSProcessInfo+MGLAdditions.m

@@ -1,15 +1,9 @@
 #import "NSProcessInfo+MGLAdditions.h"
 
-#if TARGET_OS_IPHONE || TARGET_OS_SIMULATOR
-    static NSString * const MGLIBDesignablesAgentProcessName = @"IBDesignablesAgentCocoaTouch";
-#elif TARGET_OS_MAC
-    static NSString * const MGLIBDesignablesAgentProcessName = @"IBDesignablesAgent";
-#endif
-
 @implementation NSProcessInfo (MGLAdditions)
 
 - (BOOL)mgl_isInterfaceBuilderDesignablesAgent {
-    return [self.processName isEqualToString:MGLIBDesignablesAgentProcessName];
+    return [self.processName hasPrefix:@"IBDesignablesAgent"];
 }
 
 @end

platform/macos/CHANGELOG.md

@@ -5,6 +5,7 @@
 ### Packaging
 
 * The minimum deployment target for this SDK is now macOS 10.11.0. ([#11776](https://github.com/mapbox/mapbox-gl-native/pull/11776))
+* Fixed an issue where `MGLMapView` produced a designable error in Interface Builder storyboards. ([#12140](https://github.com/mapbox/mapbox-gl-native/pull/12140))
 
 ### Style layers