Rollup merge of #22339 - petrochenkov:int, r=huonw

Some function signatures have changed, so this is a [breaking-change].
In particular, radixes and numerical values of digits are represented by `u32` now.

Part of #22240

src/libsyntax/parse/lexer/mod.rs

@@ -645,7 +645,7 @@ impl<'a> StringReader<'a> {
 
     /// Scan through any digits (base `radix`) or underscores, and return how
     /// many digits there were.
-    fn scan_digits(&mut self, radix: usize) -> usize {
+    fn scan_digits(&mut self, radix: u32) -> usize {
         let mut len = 0;
         loop {
             let c = self.curr;