On a hot path, the probe can record every hit and require
filtering afterwards. This patch adds a per-probe `--cond <expr>`
option that allows limiting the hit to only when the expression
is truthy at the probe location. V8 evaluates it as the breakpoint's
native condition, so the target is not paused when it does not hold,
and a condition that throws is treated as false. Since in CDP,
a location can only carry one breakpoint per URL pattern,
probes sharing a location must share one condition (or none).
Conflicting conditions are rejected.

Example:

```js
// app.js
let total = 0;
for (let i = 0; i < 10; i++) {
  total += i;  // line 4
}
```

```
$ out/Release/node inspect --probe app.js:4 --expr 'total' \
                           --cond 'i % 3 === 0' app.js
```

```
Hit 1 at file:///path/to/app.js:3:3
  total = 0
Hit 2 at file:///path/to/app.js:3:3
  total = 3
Hit 3 at file:///path/to/app.js:3:3
  total = 15
Hit 4 at file:///path/to/app.js:3:3
  total = 36
Completed
```

Signed-off-by: Joyee Cheung <joyeec9h3@gmail.com>