Convert many functions to use StringRefs.

Where possible, remove the const char* version.  To keep the
risk and impact here minimal, I've only done the simplest
functions.

In the process, I found a few opportunities for adding some
unit tests, so I added those as well.

Tested on Windows, Linux, and OSX.

llvm-svn: 281799
diff --git a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp
index e554faf..a18ab22 100644
--- a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp
+++ b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp
@@ -1194,8 +1194,8 @@
                                      // "version" key instead of
                                      // "os_version"...
           {
-            Args::StringToVersion(value.str().c_str(), m_os_version_major,
-                                  m_os_version_minor, m_os_version_update);
+            Args::StringToVersion(value, m_os_version_major, m_os_version_minor,
+                                  m_os_version_update);
             if (m_os_version_major != UINT32_MAX)
               ++num_keys_decoded;
           } else if (name.equals("watchpoint_exceptions_received")) {