[platform process list] add a flag for showing the processes of all users
Summary:
For context: https://reviews.llvm.org/D68293
We need a way to show all the processes on android regardless of the user id.
When you run `platform process list`, you only see the processes with the same user as the user that launched lldb-server. However, it's quite useful to see all the processes, though, and it will lay a foundation for full apk debugging support from lldb.
Before:
```
PID PARENT USER TRIPLE NAME
====== ====== ========== ======================== ============================
3234 1 aarch64-unknown-linux-android adbd
8034 3234 aarch64-unknown-linux-android sh
9096 3234 aarch64-unknown-linux-android sh
9098 9096 aarch64-unknown-linux-android lldb-server
(lldb) ^D
```
Now:
```
(lldb) platform process list -x
205 matching processes were found on "remote-android"
PID PARENT USER TRIPLE NAME
====== ====== ========== ======================== ============================
1 0 init
524 1 init
525 1 init
531 1 ueventd
568 1 logd
569 1 aarch64-unknown-linux-android servicemanager
570 1 aarch64-unknown-linux-android hwservicemanager
571 1 aarch64-unknown-linux-android vndservicemanager
577 1 aarch64-unknown-linux-android qseecomd
580 577 aarch64-unknown-linux-android qseecomd
...
23816 979 com.android.providers.calendar
24600 979 com.verizon.mips.services
27888 979 com.hualai
28043 2378 com.android.chrome:sandboxed_process0
31449 979 com.att.shm
31779 979 com.samsung.android.authfw
31846 979 com.samsung.android.server.iris
32014 979 com.samsung.android.MtpApplication
32045 979 com.samsung.InputEventApp
```
Reviewers: labath,xiaobai,aadsm,clayborg
Subscribers:
> llvm-svn: 374584
llvm-svn: 374626