[Feature #19755]

Before (in /tmp/test.rb):

```ruby
Object.class_eval("p __FILE__") # => "(eval)"
```

After:

```ruby
Object.class_eval("p __FILE__") # => "(eval at /tmp/test.rb:1)"
```

This makes it much easier to track down generated code in case
the author forgot to provide a filename argument.

Co-authored-by: Benoit Daloze <eregontp@gmail.com>

If TracePoint#enable is passed a block, it previously started
the trace on all threads.  This changes it to trace only the
current thread by default.  To limit the scope of the change,
the current thread is only used by default if target and
target_line are both nil.  You can pass target_thread: nil
to enable tracing on all threads, to get the previous
default behavior.

Fixes [Bug #16889]

This updates the trace instructions to directly dispatch to
opt_send_without_block.  So this should cause no slowdown in
non-trace mode.

To enable the tracing of the optimized methods, RUBY_EVENT_C_CALL
and RUBY_EVENT_C_RETURN are added as events to the specialized
instructions.

Fixes [Bug #14870]

Co-authored-by: Takashi Kokubun <takashikkbn@gmail.com>