Add a codegen tool to generate a fast switch-tree interpreter dispatcher

MIPSTables.cpp has walked a tree of tables on every single interpreted
instruction since forever, with a standing TODO asking for exactly this:
"generate smart dispatcher functions from above tables instead of this
slow method." GenerateInterpreterDispatch() does that - it walks the
same tables MIPSGetInstruction() walks at runtime, but resolves the
walk into a nested switch tree once, at generation time, with each
leaf calling straight into the existing MIPSInt::Int_* handlers and
returning that instruction's fixed cycle count. Anything not covered
(invalid opcodes, and the handful of instructions with no interpreter
implemented at all, e.g. tge/tlt/teq) falls back to the existing
MIPSInterpret()/MIPSGetInstructionCycleEstimate() slow path, so the
result is total over all 32-bit inputs, same as the table-walking path.

Wired up via a new headless --generate-interpreter-dispatch flag,
which prints the generated Core/MIPS/InterpreterDispatch.cpp source to
stdout and exits.

Also widens CmdLine.cpp's --help column formatting, which silently
truncated any option name longer than 24 characters - the new option's
name was the first to hit it.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_019SKhm9wKEQzRUsx9mTrrtQ

headless/Headless.cpp

@@ -54,6 +54,7 @@
 #include "Core/Core.h"
 #include "Core/CoreTiming.h"
 #include "Core/EmuThread.h"
+#include "Core/MIPS/MIPSTables.h"
 #include "Core/System.h"
 #include "Core/WebServer.h"
 #include "Core/HLE/sceUtility.h"
@@ -550,6 +551,12 @@ int main(int argc, const char* argv[]) {
 		break;
 	}
 
+	if (cmdLineOptions.generateInterpreterDispatch.value_or(false)) {
+		std::string code = GenerateInterpreterDispatch();
+		fwrite(code.data(), 1, code.size(), stdout);
+		return 0;
+	}
+
 	// Needed before any sockets can be used (WSAStartup on Windows) - without this, the
 	// WebSocket debugger silently fails to listen. Only done when requested since headless
 	// otherwise has no use for networking.