Change `dwim-print` to now disable persistent results by default, unless requested by
the user with the `--persistent-result` flag.
Ex:
```
(lldb) dwim-print 1 + 1
(int) 2
(lldb) dwim-print --persistent-result on -- 1 + 1
(int) $0 = 2
```
Users who wish to enable persistent results can make and use an alias that includes
`--persistent-result on`.
Updates: To recommit this, both TestPersistentResult.py and TestPAlias.py needed to be
updated, as well as the changes in D146230.
Differential Revision: https://reviews.llvm.org/D145609
In API tests, replace use of the `p` alias with the `expression` command.
To avoid conflating tests of the alias with tests of the expression command,
this patch canonicalizes to the use `expression`.
Differential Revision: https://reviews.llvm.org/D141539
