PHP: `pecl install` is still slow and still produces massive binaries

### What version of gRPC and what language are you using?

- All versions of gRPC
- PHP

### What operating system (Linux, Windows,...) and version?

- Linux (all versions)

### What runtime / compiler are you using (e.g. python version or version of gcc)

- pecl (all versions)

### What did you do?
Please provide either 1) A unit test for reproducing the bug or 2) Specific steps for us to follow to reproduce the bug. If there’s not enough information to debug the problem, gRPC team may close the issue at their discretion. You’re welcome to re-open the issue once you have a reproduction.

```shell
time sudo pecl install grpc
```

### What did you expect to see?

The extension install in a reasonable timeframe and at a reasonable size

### What did you see instead?

The extension install takes on the order of 30 minutes, and produces a ~50MB binary that is ~10x larger than intended due to the inclusion of debug symbols (which should not be present in builds created or distributed this way).

Make sure you include information that can help us debug (full error message, exception listing, stack trace, logs).

See [TROUBLESHOOTING.md](https://github.com/grpc/grpc/blob/master/TROUBLESHOOTING.md) for how to diagnose problems better.

### Anything else we should know about your project / environment?

Please see the existing discussion at #23626.

I'm opening this as a new Issue because the previous one was closed seemingly by accident (and I lack the permissions to reopen it). If that Issue can be reopened, this one can be closed as a duplicate. Until then, the problem risks not being tracked or mitigated.