Add testcase for next_point, fix more trivial issues in find_width_of_character_at_span

Author: chenyukang

clippy_utils/src/sugg.rs

@@ -769,8 +769,7 @@ impl<T: LintContext> DiagnosticExt<T> for rustc_errors::Diagnostic {
 
     fn suggest_remove_item(&mut self, cx: &T, item: Span, msg: &str, applicability: Applicability) {
         let mut remove_span = item;
-        let hi = cx.sess().source_map().next_point(remove_span).hi();
-        let fmpos = cx.sess().source_map().lookup_byte_offset(hi);
+        let fmpos = cx.sess().source_map().lookup_byte_offset(remove_span.hi());
 
         if let Some(ref src) = fmpos.sf.src {
             let non_whitespace_offset = src[fmpos.pos.to_usize()..].find(|c| c != ' ' && c != '\t' && c != '\n');