[Common tests] Support RENDER_ALL_DIAGNOSTICS_FULL_TEXT in JS BE tests

Move the checkFullDiagnosticRender() function from
the JvmBackendDiagnosticsHandler class so it can be reused
in the JsBackendDiagnosticsHandler class.

js/js.tests/test/org/jetbrains/kotlin/js/test/handlers/JsBackendDiagnosticsHandler.kt

@@ -6,6 +6,7 @@
 package org.jetbrains.kotlin.js.test.handlers
 
 import org.jetbrains.kotlin.test.backend.handlers.KlibArtifactHandler
+import org.jetbrains.kotlin.test.backend.handlers.checkFullDiagnosticRender
 import org.jetbrains.kotlin.test.backend.handlers.reportKtDiagnostics
 import org.jetbrains.kotlin.test.model.BinaryArtifacts
 import org.jetbrains.kotlin.test.model.TestModule
@@ -14,6 +15,7 @@ import org.jetbrains.kotlin.test.services.*
 class JsBackendDiagnosticsHandler(testServices: TestServices) : KlibArtifactHandler(testServices) {
     override fun processModule(module: TestModule, info: BinaryArtifacts.KLib) {
         reportKtDiagnostics(module, info.reporter)
+        checkFullDiagnosticRender(module)
     }
 
     override fun processAfterAllModules(someAssertionWasFailed: Boolean) {}