Declare other tokens used later in the reference grammar

There were some tokens used in the grammar but not declared. Antlr
doesn't really seem to care and happily uses them, but they appear in
RustLexer.tokens in a potentially-unexpected order.

src/grammar/RustLexer.g4

@@ -12,10 +12,10 @@ tokens {
     MINUS, STAR, SLASH, PERCENT, CARET, AND, OR, SHL, SHR, BINOP,
     BINOPEQ, AT, DOT, DOTDOT, DOTDOTDOT, COMMA, SEMI, COLON,
     MOD_SEP, RARROW, FAT_ARROW, LPAREN, RPAREN, LBRACKET, RBRACKET,
-    LBRACE, RBRACE, POUND, DOLLAR, UNDERSCORE, LIT_CHAR,
+    LBRACE, RBRACE, POUND, DOLLAR, UNDERSCORE, LIT_CHAR, LIT_BYTE,
     LIT_INTEGER, LIT_FLOAT, LIT_STR, LIT_STR_RAW, LIT_BINARY,
-    LIT_BINARY_RAW, IDENT, LIFETIME, WHITESPACE, DOC_COMMENT,
-    COMMENT, SHEBANG
+    LIT_BINARY_RAW, QUESTION, IDENT, LIFETIME, WHITESPACE, DOC_COMMENT,
+    COMMENT, SHEBANG, UTF8_BOM
 }
 
 import xidstart , xidcontinue;