Load async-profiler.jar if possible when using -Xprofile

Instead of requiring it to be on the compiler classpath.

This will make it much easier to profile the Kotlin compiler daemon in
Gradle, by just specifying a compiler argument instead of also manually
patching the compiler jar.

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

@@ -452,9 +452,9 @@ default: `indy-with-constants` for JVM target 9 or greater, `inline` otherwise""
     @Argument(
         value = "-Xprofile",
         valueDescription = "<profilerPath:command:outputDir>",
-        description = "Debug option: Run compiler with async profiler, save snapshots to outputDir, command is passed to async-profiler on start\n" +
-                "You'll have to provide async-profiler.jar on classpath to use this\n" +
-                "profilerPath is a path to libasyncProfiler.so\n" +
+        description = "Debug option: Run compiler with async profiler and save snapshots to `outputDir`; `command` is passed to async-profiler on start.\n" +
+                "`profilerPath` is a path to libasyncProfiler.so; async-profiler.jar should be on the compiler classpath.\n" +
+                "If it's not on the classpath, the compiler will attempt to load async-profiler.jar from the containing directory of profilerPath.\n" +
                 "Example: -Xprofile=<PATH_TO_ASYNC_PROFILER>/async-profiler/build/libasyncProfiler.so:event=cpu,interval=1ms,threads,start,framebuf=50000000:<SNAPSHOT_DIR_PATH>"
     )
     var profileCompilerCommand: String? by NullableStringFreezableVar(null)