Print methods in exception messages in java-like Syntax.

A row of exceptions are thrown from the hotspot runtime.
They print methods with their JNI signatures. To increase
readability and resemblance to source code, print them
in a Java-like syntax.

Some examples:

current method printouts:

test.TeMe3_B.ma()V
test.TeMe3_B.ma(IZ[[BF)[[D
test.TeMe3_B.ma([[[Ljava/lang/Object;)[[Ltest/TeMe3_B;

improved format:

void test.TeMe3_B.ma()
double[][] test.TeMe3_B.ma(int, boolean, byte[][], float)
test.TeMe3_B[][] test.TeMe3_B.ma(java.lang.Object[][][])

So far, Method::name_and_sig_as_C_string() is used to print
these messages.

Implement function Method::external_name() that prints the better
format.
external_name() is chosen according to Klass::external_name().

Printing the better format requires parsing the signature
Symbol. This is implemented in
void Symbol::print_as_signature_external_return_type(outputStream *os);
void Symbol::print_as_signature_external_parameters(outputStream *os);
These method names are chosen according to Symbol::as_class_external_name().

Adapt printing messages and according tests.