Implicit const char* cast removed, operator<< added to hidl_string.

hidl_string no longer will provide an implicit cast to const char* as it
interfers with other expected behaviors of the class.  It now emulated
std::string in requiring a call to .c_str() to get the same behavior.

Bug:  36532780
Test:  Build the tree for marlin, bullhead, bat

(cherry picked from commit 0c84ab4192f9b0b03b9840b85fc430afa17f55f1)

Merged-In: I6ba76522ef65aa211bc156144990ad8b7495b051
Change-Id: I6ba76522ef65aa211bc156144990ad8b7495b051
diff --git a/base/HidlSupport.cpp b/base/HidlSupport.cpp
index 5789d04..7cc8ef5 100644
--- a/base/HidlSupport.cpp
+++ b/base/HidlSupport.cpp
@@ -208,8 +208,9 @@
     return std::string(mBuffer, mSize);
 }
 
-hidl_string::operator const char *() const {
-    return mBuffer;
+std::ostream& operator<<(std::ostream& os, const hidl_string& str) {
+    os << str.c_str();
+    return os;
 }
 
 void hidl_string::copyFrom(const char *data, size_t size) {