cppia: a debugger that attaches before a script loads cannot set breakpoints in it #283

Checked end to end with the VS Code hxcpp debugger's server (hxcpp-debug-server 1.2.4, stock) and a host built with -debug -D scriptable -lib hxcpp-debug-server, on Windows. A breakpoint in the script comes back as -1 and the script runs straight through, interpreted and with the JIT.

The server starts with the host and attaches before any script is loaded. It reads Debugger.getFiles() once, as it attaches, so the script's files are never in its list, and it has no way to learn when they arrive: hxcpp's callback for that, __hxcpp_dbg_setOnScriptLoadedFunction (HaxeFoundation/hxcpp#1203), only exists at API level 500, so with Haxe 4 nothing tells a debugger that a script has loaded.

Our part: call the script-loaded callback at every API level, after a script loads and before it boots, and give C++ a macro to test for it, so a server that also builds against other hxcpp versions can use it. The server's part, reading its files again in the callback and setting the breakpoints that were waiting, is a change to vshaxe/hxcpp-debugger.

With both, breakpoints, stepping over and out, and locals work in a script from the debugger's protocol, in the interpreter and with the JIT, whether the breakpoint was set before the script loaded or while it ran.