Restore blue-painting of macro arg expansions to prevent recursion

src/asm/lexer.cpp

@@ -817,6 +817,11 @@ static int peek() {
 			shiftChar();
 			if (std::shared_ptr<std::string> str = readMacroArg(); str) {
 				beginExpansion(str, std::nullopt);
+
+				// Mark the entire macro arg expansion as "painted blue"
+				// so that macro args can't be recursive
+				// https://en.wikipedia.org/wiki/Painted_blue
+				lexerState->macroArgScanDistance += str->length();
 			}
 		} else if (c == '{' && !lexerState->disableInterpolation) {
 			// If character is an open brace, do symbol interpolation

test/asm/macro-arg-recursion.asm

@@ -0,0 +1,6 @@
+MACRO m
+	def x = (\1) * 2
+	println "{d:x}"
+ENDM
+	m 5       ; prints 10
+	m \\2, 6  ; should not prints 12

test/asm/macro-arg-recursion.err

@@ -0,0 +1,3 @@
+error: macro-arg-recursion.asm(6) -> macro-arg-recursion.asm::m(2):
+    Begun line continuation, but encountered character '2'
+Assembly aborted with 1 error!

test/asm/macro-arg-recursion.out

@@ -0,0 +1,2 @@
+10
+4