Fix code analysis C4018 warnings (#3223)

* Replace `auto`s with `size_t`s to reduce:

```
Severity	Code	Description	Project	File	Line	Suppression State
Warning	C4018	'<': signed/unsigned mismatch	CefSharp.BrowserSubprocess.Core	c:\repos\cefsharp\cefsharp.browsersubprocess.core\serialization\jsobjectsserialization.cpp	71
```

* Fix templates