Tokenizing fallibility (#883)

Tokenization tracks invalid tokens and produces a nice error about them

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Co-authored-by: Adam Chalmers <adam.chalmers@kittycad.io>

src/lang/errors.ts

@@ -18,6 +18,13 @@ export class KCLError {
   }
 }
 
+export class KCLLexicalError extends KCLError {
+  constructor(msg: string, sourceRanges: [number, number][]) {
+    super('lexical', msg, sourceRanges)
+    Object.setPrototypeOf(this, KCLSyntaxError.prototype)
+  }
+}
+
 export class KCLSyntaxError extends KCLError {
   constructor(msg: string, sourceRanges: [number, number][]) {
     super('syntax', msg, sourceRanges)