Mass rewrite dtors to use "= default".

A simple search and replace with sed s/::~\(.*\) {}$/::~\1 = default;/
works surprisingly well.

Change-Id: Ie958265266e504006061e8f1b957046dfecd70dc
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/70251
Reviewed-by: Daniel Hosseinian <dhoss@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
diff --git a/core/fxcrt/widestring.cpp b/core/fxcrt/widestring.cpp
index 10a31c3..2855cc9 100644
--- a/core/fxcrt/widestring.cpp
+++ b/core/fxcrt/widestring.cpp
@@ -383,7 +383,7 @@
   }
 }
 
-WideString::~WideString() {}
+WideString::~WideString() = default;
 
 WideString& WideString::operator=(const wchar_t* str) {
   if (!str || !str[0])