Fix missing class in manifest merger

If manifest merger sees a manifest with an sdk codename instead
of a number it fails with:
Exception in thread "main" java.lang.NoClassDefFoundError: com/android/sdklib/SdkVersionInfo
	at com.android.manifmerger.XmlDocument.getApiLevelFromAttribute(XmlDocument.java:384)
	at com.android.manifmerger.XmlDocument.addImplicitElements(XmlDocument.java:418)
	at com.android.manifmerger.XmlDocument.merge(XmlDocument.java:161)
	at com.android.manifmerger.ManifestMerger2.merge(ManifestMerger2.java:909)
	at com.android.manifmerger.ManifestMerger2.merge(ManifestMerger2.java:263)
	at com.android.manifmerger.ManifestMerger2.access$600(ManifestMerger2.java:61)
	at com.android.manifmerger.ManifestMerger2$Invoker.merge(ManifestMerger2.java:1530)
	at com.android.manifmerger.Merger.process(Merger.java:153)
	at com.android.manifmerger.Merger.main(Merger.java:42)
Caused by: java.lang.ClassNotFoundException: com.android.sdklib.SdkVersionInfo
	at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:582)
	at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:185)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:496)
	... 9 more

Add sdklib to the classpath to fix it.

Test: m java
Bug: 77569197
Change-Id: I54fd9edb36aca32cff507340a76eee5e367529e6