Syntax errors resets the lexer right away

`DEF`, `REDEF`, etc disable EQUS expansion, and reading
macro or OPT arguments sets the lexer to raw mode.
Syntax errors resume normal parsing at the line's end,
but should resume normal tokenization even before that.

test/asm/syntax-error-lexer-mode.asm

@@ -0,0 +1,12 @@
+newline equs "\n"
+
+def x = 1 newline def y = 2
+println "x={d:x}, y={d:y}"
+
+; the lexer is already in normal mode at the `AF`, so `newline` gets expanded
+def m = AF newline def n = 2
+println "n={d:n}"
+
+; the lexer is in raw mode at the `AF`, but the parser resets it to normal
+def AF = 1 newline def q = 2
+println "q={d:q}"

test/asm/syntax-error-lexer-mode.err

@@ -0,0 +1,5 @@
+ERROR: syntax-error-lexer-mode.asm(7):
+    syntax error, unexpected af
+ERROR: syntax-error-lexer-mode.asm(11):
+    syntax error, unexpected af, expecting identifier
+error: Assembly aborted (2 errors)!

test/asm/syntax-error-lexer-mode.out

@@ -0,0 +1,3 @@
+x=1, y=2
+n=2
+q=2