[lldb] Redefine p alias to dwim-print command

Redefine the `p` alias to the `dwim-print` command instead of `expression`.

See https://reviews.llvm.org/D138315 for the introduction of `dwim-print`.

To summarize, `dwim-print` is, as the name suggests, a command for printing. How a value
gets printed, is decided by `dwim-print`. In some cases, `dwim-print` will print values
using the same means as `frame variable` (because it's generally more reliable and
faster that `expression` evaluation), and in other cases `dwim-print` uses the same code
path as `expression`.

This change has been tested in two different ways:

1. Re-aliasing `p` to `dwim-print`, as in this patch
2. Redefinining the `expression` command to `CommandObjectDWIMPrint`

Previously, many of the lldb's tests used `p`, and which meant a test run with `p`
aliases to `dwim-print` was a good way to test `dwim-print`. However most of those tests
were updated to use `expression` explicitly (in anticipation of this change). Now, the
best way to test `dwim-print` is the second approach:

```
diff --git a/lldb/source/Interpreter/CommandInterpreter.cpp b/lldb/source/Interpreter/CommandInterpreter.cpp
index 373c894f34f5..9c943cd30c7c 100644
--- a/lldb/source/Interpreter/CommandInterpreter.cpp
+++ b/lldb/source/Interpreter/CommandInterpreter.cpp
@@ -539,7 +539,7 @@ void CommandInterpreter::LoadCommandDictionary() {
   REGISTER_COMMAND_OBJECT("diagnostics", CommandObjectDiagnostics);
   REGISTER_COMMAND_OBJECT("disassemble", CommandObjectDisassemble);
   REGISTER_COMMAND_OBJECT("dwim-print", CommandObjectDWIMPrint);
-  REGISTER_COMMAND_OBJECT("expression", CommandObjectExpression);
+  REGISTER_COMMAND_OBJECT("expression", CommandObjectDWIMPrint);
   REGISTER_COMMAND_OBJECT("frame", CommandObjectMultiwordFrame);
   REGISTER_COMMAND_OBJECT("gui", CommandObjectGUI);
   REGISTER_COMMAND_OBJECT("help", CommandObjectHelp);
```

When the test suite is run with this change, there are two main categories of test
failures for specific to features that `dwim-print` intentionally doesn't support:

1. Top level expressions (`--top-level`/`-p`)
2. Multiline expressions

In cases where the behavior of `expression` is needed, users can use `expression` at
those times.

Differential Revision: https://reviews.llvm.org/D145189