Fix running the XSLT tests on IntelliJ 2025.3.

Author: rhdunn

src/intellij-test/compat/251-253/253/uk/co/reecedunn/intellij/plugin/core/tests/xml/Requires.kt

@@ -5,6 +5,12 @@ import com.intellij.ide.highlighter.XmlFileType
 import com.intellij.lang.xml.XMLLanguage
 import com.intellij.lang.xml.XMLParserDefinition
 import com.intellij.lang.xml.XmlASTFactory
+import com.intellij.lang.xml.XmlSyntaxDefinitionExtension
+import com.intellij.platform.syntax.psi.ElementTypeConverter
+import com.intellij.platform.syntax.psi.ElementTypeConverterFactory
+import com.intellij.platform.syntax.psi.ElementTypeConverters
+import com.intellij.platform.syntax.psi.LanguageSyntaxDefinitions
+import com.intellij.psi.xml.xmlElementTypeConverter
 import com.intellij.xml.XmlExtension
 import uk.co.reecedunn.intellij.plugin.core.extensions.registerExtensionPointBean
 import uk.co.reecedunn.intellij.plugin.core.tests.lang.registerExtension
@@ -20,4 +26,10 @@ fun PlatformTestCase.requiresXmlParser() {
     app.registerExtensionPointBean(XmlExtension.EP_NAME, XmlExtension::class.java, pluginDisposable)
 
     requiresPsiSyntaxBuilderFactory()
+
+    ElementTypeConverters.instance.addExplicitExtension(XMLLanguage.INSTANCE, object : ElementTypeConverterFactory {
+        override fun getElementTypeConverter(): ElementTypeConverter = xmlElementTypeConverter
+    })
+
+    LanguageSyntaxDefinitions.INSTANCE.addExplicitExtension(XMLLanguage.INSTANCE, XmlSyntaxDefinitionExtension())
 }

src/intellij-test/compat/253/native/uk/co/reecedunn/intellij/plugin/core/tests/syntax/Requires.kt

@@ -1,10 +1,14 @@
 // Copyright (C) 2025 Reece H. Dunn. SPDX-License-Identifier: Apache-2.0
 package uk.co.reecedunn.intellij.plugin.core.tests.syntax
 
+import com.intellij.lang.MetaLanguage
 import com.intellij.platform.syntax.psi.PsiSyntaxBuilderFactory
+import uk.co.reecedunn.intellij.plugin.core.extensions.registerExtensionPointBean
 import uk.co.reecedunn.intellij.plugin.core.extensions.registerService
 import uk.co.reecedunn.intellij.plugin.core.tests.testFramework.PlatformTestCase
 
 fun PlatformTestCase.requiresPsiSyntaxBuilderFactory() {
+    app.registerExtensionPointBean(MetaLanguage.EP_NAME, MetaLanguage::class.java, pluginDisposable)
+
     app.registerService(PsiSyntaxBuilderFactory.defaultBuilderFactory())
 }