cppia: locals and continuing break with hxcpp master; breakpoints stay unverified #4

With vshaxe#48 merged (5660aa5) and the file mapping fix (14a4e50), a debug cppia host stops at breakpoints in a script it loads. How well that works depends on the runtime:

• libhxcpp main (2573b94) with Haxe 4.3.7: breakpoints, stepping, locals and the console work.
• hxcpp master (504403d) with the Haxe 5 preview: a breakpoint stops at the right line with the right stack, but locals read as 0 (a=0 b=0 instead of 2 and 3), and after continuing the host exits with code 1 and prints nothing more.
• hxcpp 4.3.2, or git hxcpp with Haxe 4: there's no script-loaded callback (__hxcpp_dbg_setOnScriptLoadedFunction exists only at HXCPP_API_LEVEL 500 or above), so breakpoints set before the script loads never take effect.

Also:

• A breakpoint on return a + b; in a script stops twice per call.
• The server can't tell the debugger when a waiting breakpoint takes effect, so the editor keeps showing it as unverified. A notification from the server when onScriptLoaded sets breakpoints would fix that.

Setup used: the host is cpp.cppia.Host.runFile(Sys.args()[0]), built with -D scriptable --cpp host -debug -cp <hxcpp-debug-server> --macro hxcpp.debug.jsonrpc.Macro.injectServer(). The script is built with --cppia script.cppia -debug.