Enhance TRACE_METHOD_LINKAGE to show the target MethodHandle

Improve the handling of the java.lang.invoke.MethodHandle.TRACE_METHOD_LINKAGE property to print out the full graph of MethodHandles that are used at a CallSite. This helps us understand how invokedynamic call sites are resolved. For example:

public class StrConcat {
    static String hello = "Hello";
    static String world = "World";
    public static void main(String args[]) {
        System.out.println(hello + world);
        System.out.println(hello + "World");
    }
}

$ java -Djava.lang.invoke.MethodHandle.TRACE_METHOD_LINKAGE=true -cp . StrConcat
linkCallSite StrConcat.main(StrConcat.java:5) java.lang.invoke.StringConcatFactory.makeConcatWithConstants(Lookup,String,MethodType,String,Object[])CallSite/invokeStatic makeConcatWithConstants(String,String)String/BSA1=
linkMethod java.lang.invoke.MethodHandle.invokeExact(Lookup,String,MethodType,String,Object[])CallSite/5
linkMethod => java.lang.invoke.Invokers$Holder.invokeExact_MT(Object,Object,Object,Object,Object,Object,Object)Object/invokeStatic + (Lookup,String,MethodType,String,Object[])CallSite
linkCallSite target class => java.lang.invoke.BoundMethodHandle$Species_L
linkCallSite target => (String,String)String : BMH.reinvoke000_LLL_L=Lambda(a0:L/SpeciesData[L => Species_L],a1:L,a2:L)=>{
    t3:L=Species_L.argL0(a0:L);
    t4:L=MethodHandle.invokeBasic(t3:L,a1:L,a2:L);t4:L}
& BMH=[
  0: MethodHandle = {(Object,Object)String : DMH.invokeStatic000_LLL_L=Lambda(a0:L,a1:L,a2:L)=>{
        t3:L=DirectMethodHandle.internalMemberName(a0:L);
        t4:L=MethodHandle.linkToStatic(a1:L,a2:L,t3:L);t4:L}
    & DMH.MN=java.lang.StringConcatHelper.simpleConcat(Object,Object)String/invokeStatic
  }
]
linkCallSite linkage => java.lang.invoke.Invokers$Holder.linkToTargetMethod(Object,Object,Object)Object/invokeStatic + MethodHandle(String,String)String
HelloWorld
linkCallSite StrConcat.main(StrConcat.java:6) java.lang.invoke.StringConcatFactory.makeConcatWithConstants(Lookup,String,MethodType,String,Object[])CallSite/invokeStatic makeConcatWithConstants(String)String/BSA1=World
linkCallSite target class => java.lang.invoke.BoundMethodHandle$Species_LL
linkCallSite target => (String)String : invoke000_LL_L=Lambda(a0:L/SpeciesData[LL => BoundMethodHandle$Species_LL],a1:L)=>{
    t2:L=BoundMethodHandle$Species_LL.argL1(a0:L);
    t3:L=BoundMethodHandle$Species_LL.argL0(a0:L);
    t4:L=MethodHandle.invokeBasic(t3:L,a1:L,t2:L);t4:L}
& BMH=[
  0: MethodHandle = {(Object,Object)String : DMH.invokeStatic000_LLL_L=Lambda(a0:L,a1:L,a2:L)=>{
        t3:L=DirectMethodHandle.internalMemberName(a0:L);
        t4:L=MethodHandle.linkToStatic(a1:L,a2:L,t3:L);t4:L}
    & DMH.MN=java.lang.StringConcatHelper.simpleConcat(Object,Object)String/invokeStatic
  }
  1: ( World )
]
linkCallSite linkage => java.lang.invoke.Invokers$Holder.linkToTargetMethod(Object,Object)Object/invokeStatic + MethodHandle(String)String
HelloWorld

********************************************************************

By human parsing, we can see that the first call site at StrConcat.java:5 is resolved to:

    MethodHandle mh = a0.argL0; // DirectMethodHandle of simpleConcat(Object,Object)
    invoke mh with (a1, a2); // a1 = StrConcat.hello; a2 = StrConcat.world
    return the result of the mh invocation

The second callsite is similar, except the second argument to the simpleConcat() call is taken from a0.argL1 (the constant "World").