Allow lexer to recover from some homoglyphs

src/test/ui/parser/recover-from-homoglyph.rs

@@ -0,0 +1,4 @@
+fn main() {
+    println!(""); //~ ERROR unknown start of token: \u{37e}
+    let x: usize = (); //~ ERROR mismatched types
+}

src/test/ui/parser/recover-from-homoglyph.stderr

@@ -0,0 +1,22 @@
+error: unknown start of token: \u{37e}
+  --> $DIR/recover-from-homoglyph.rs:2:17
+   |
+LL |     println!("");
+   |                 ^
+help: Unicode character ';' (Greek Question Mark) looks like ';' (Semicolon), but it is not
+   |
+LL |     println!("");
+   |                 ^
+
+error[E0308]: mismatched types
+  --> $DIR/recover-from-homoglyph.rs:3:20
+   |
+LL |     let x: usize = ();
+   |                    ^^ expected usize, found ()
+   |
+   = note: expected type `usize`
+              found type `()`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0308`.