[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

(cherry picked from commit a00801d)

Author: kastiglione

lldb/source/Interpreter/CommandInterpreter.cpp

@@ -412,24 +412,21 @@ void CommandInterpreter::Initialize() {
 
   alias_arguments_vector_sp = std::make_shared<OptionArgVector>();
 
-  cmd_obj_sp = GetCommandSPExact("expression");
+  cmd_obj_sp = GetCommandSPExact("dwim-print");
   if (cmd_obj_sp) {
     AddAlias("p", cmd_obj_sp, "--")->SetHelpLong("");
     AddAlias("print", cmd_obj_sp, "--")->SetHelpLong("");
-    AddAlias("call", cmd_obj_sp, "--")->SetHelpLong("");
     if (auto *po = AddAlias("po", cmd_obj_sp, "-O --")) {
       po->SetHelp("Evaluate an expression on the current thread.  Displays any "
                   "returned value with formatting "
                   "controlled by the type's author.");
       po->SetHelpLong("");
     }
+  }
 
-#ifdef LLDB_ENABLE_SWIFT
-    // FIXME: Upstream the REPL command together with support for a default
-    // language, similar to what exists for scripting.
-    AddAlias("repl", cmd_obj_sp, "--repl --language swift -- ");
-#endif
-
+  cmd_obj_sp = GetCommandSPExact("expression");
+  if (cmd_obj_sp) {
+    AddAlias("call", cmd_obj_sp, "--")->SetHelpLong("");
     CommandAlias *parray_alias =
         AddAlias("parray", cmd_obj_sp, "--element-count %1 --");
     if (parray_alias) {
@@ -447,6 +444,12 @@ void CommandInterpreter::Initialize() {
           "objects in memory, and will call po on them.");
       poarray_alias->SetHelpLong("");
     }
+
+#ifdef LLDB_ENABLE_SWIFT
+    // FIXME: Upstream the REPL command together with support for a default
+    // language, similar to what exists for scripting.
+    AddAlias("repl", cmd_obj_sp, "--repl --language swift -- ");
+#endif
   }
 
   cmd_obj_sp = GetCommandSPExact("platform shell");