[lldb-dap] Improving 'variables' hover requests.

This partially fixes #146559.

When hovering over variables while debugging with lldb-dap we are
receiving hover requests that include symbols.

For example, if you have:

```
MyClass *foo;
```

and hover over 'foo', the request will contain the expression
`expression="*foo"` and we're evaluating the dereference, so you end up
with different hover results vs the variables view.

A more complete solution would be to implement an
[EvaluatableExpressionProvider](https://code.visualstudio.com/api/references/vscode-api#EvaluatableExpressionProvider)
in the VS Code extension.

For example, if you have a declaration without any whitespace like

```c
char*foo = "bar";
```

And try to hover over 'foo', the request will be `expression="char*foo"`.

Author: ashgti

lldb/test/API/tools/lldb-dap/memory/TestDAP_memory.py

@@ -92,7 +92,7 @@ def test_readMemory(self):
         )
         self.continue_to_next_stop()
 
-        ptr_deref = self.dap_server.request_evaluate("*rawptr")["body"]
+        ptr_deref = self.dap_server.request_evaluate("*rawptr", context="repl")["body"]
         memref = ptr_deref["memoryReference"]
 
         # We can read the complete string

lldb/tools/lldb-dap/Handler/EvaluateRequestHandler.cpp

@@ -181,7 +181,17 @@ void EvaluateRequestHandler::operator()(
         expression = dap.last_nonempty_var_expression;
       else
         dap.last_nonempty_var_expression = expression;
+    } else {
+      // If this isn't a REPL context, trim leading pointer/reference characters
+      // to ensure we return the actual value of the expression.
+      // This can come up if you hover over a pointer or reference declaration
+      // like 'MyType *foo;' or `void fn(std::string &arg)`, which results in
+      // the hover request sending '*foo' or `&arg`. When we're not in the REPL,
+      // we should trim these characters to get to the actual variable, which
+      // should have the proper type encoded by the compiler.
+      expression = llvm::StringRef(expression).ltrim("*&").str();
     }
+
     // Always try to get the answer from the local variables if possible. If
     // this fails, then if the context is not "hover", actually evaluate an
     // expression using the expression parser.