Add argument to allow running compiler without sources

`-Xbuild-file` argument allows the compiler to run without
passing any Kotlin source file in arguments.
We have been using this property in
Kotlin Gradle plugin for a few important cases:
1. incremental compilation (to update caches when there are only removed files);
2. for KAPT (Kotlin sources don't make sense in context
of running APs).

We want to stop using `-Xbuild-file` in Kotlin Gradle plugin,
and avoid breaking the Gradle plugin or IC in other build-systems.

This change adds an argument to explicitly run
the compiler without specifying any Kotlin source file.

compiler/cli/cli-common/src/org/jetbrains/kotlin/cli/common/arguments/K2JVMCompilerArguments.kt

@@ -275,6 +275,12 @@ class K2JVMCompilerArguments : CommonCompilerArguments() {
     )
     var friendPaths: Array<String>? by FreezableVar(null)
 
+    @Argument(
+        value = "-Xallow-no-source-files",
+        description = "Allow no source files"
+    )
+    var allowNoSourceFiles: Boolean by FreezableVar(false)
+
     override fun configureAnalysisFlags(collector: MessageCollector): MutableMap<AnalysisFlag<*>, Any> {
         val result = super.configureAnalysisFlags(collector)
         result[JvmAnalysisFlags.strictMetadataVersionSemantics] = strictMetadataVersionSemantics