Meta: Extend the python lexer with some more APIs

Add a few GenericLexer-style helpers to lexer.py:

* tell()
* ignore()
* next_is()

Meta/Utils/lexer.py

@@ -13,6 +13,9 @@ class Lexer:
         self.text = text
         self.position = 0
 
+    def tell(self) -> int:
+        return self.position
+
     def is_eof(self) -> bool:
         return self.position >= len(self.text)
 
@@ -35,6 +38,9 @@ class Lexer:
             return True
         return False
 
+    def next_is(self, string: str) -> bool:
+        return self.text.startswith(string, self.position)
+
     def consume_until(self, predicate: Callable[[str], bool]) -> str:
         start = self.position
         while self.position < len(self.text) and not predicate(self.text[self.position]):
@@ -47,6 +53,9 @@ class Lexer:
             self.position += 1
         return self.text[start : self.position]
 
+    def ignore(self, count: int = 1) -> None:
+        self.position = min(self.position + count, len(self.text))
+
     def ignore_until(self, ch: str) -> None:
         while self.position < len(self.text) and self.text[self.position] != ch:
             self.position += 1