gallium/android: Rewrite backtrace helper for android

The previous implementation kept a hashtable of a Backtrace object per
thread.  debug_backtrace_capture is supposed to store a backtrace in
the passed in debug_stack_frame array, but instead overwrote the
per-thread Backtrace object.

This new version works more like the libunwind based capture. We hash
the file and symbol names and store pointers in the debug_stack_frame
struct.  This way debug_backtrace_capture doesn't overwrite previous
captures or allocate memory that needs to be freed.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6112>

src/util/u_debug_stack.h

@@ -59,10 +59,12 @@ extern "C" {
  */
 struct debug_stack_frame 
 {
-#ifdef HAVE_LIBUNWIND
-   unw_word_t start_ip;
-   unsigned int off;
+#if defined(HAVE_ANDROID_PLATFORM) || defined(HAVE_LIBUNWIND)
    const char *procname;
+   uint64_t start_ip;
+   unsigned off;
+   const char *map;
+   unsigned int map_off;
 #else
    const void *function;
 #endif