fix: make find_prev_char and till_prev_char work

Bevore this PR `commands::find_prev_char` and `commands::till_prev_char` were triggerable through keys 
but `seach::find_nth_next()` was hardcoded in `_find_char`. 
The passed `fn` was nerver used. With this PR the passed `fn` is used.
The change in search.rs resolves an off by one error in the behivor of `find_nth_prev`

helix-core/src/search.rs

@@ -41,7 +41,8 @@ pub fn find_nth_prev(
     inclusive: bool,
 ) -> Option<usize> {
     // start searching right before pos
-    let mut chars = text.chars_at(pos.saturating_sub(1));
+    pos = pos.saturating_sub(1);
+    let mut chars = text.chars_at(pos);
 
     for _ in 0..n {
         loop {
@@ -56,7 +57,7 @@ pub fn find_nth_prev(
     }
 
     if !inclusive {
-        pos -= 1;
+        pos += 1;
     }
 
     Some(pos)

helix-term/src/commands.rs

@@ -315,7 +315,7 @@ fn _find_char<F>(cx: &mut Context, search_fn: F, inclusive: bool, extend: bool)
 where
     // TODO: make an options struct for and abstract this Fn into a searcher type
     // use the definition for w/b/e too
-    F: Fn(RopeSlice, char, usize, usize, bool) -> Option<usize>,
+    F: Fn(RopeSlice, char, usize, usize, bool) -> Option<usize> + 'static,
 {
     // TODO: count is reset to 1 before next key so we move it into the closure here.
     // Would be nice to carry over.
@@ -332,7 +332,7 @@ where
             let text = doc.text().slice(..);
 
             let selection = doc.selection(view.id).transform(|mut range| {
-                search::find_nth_next(text, ch, range.head, count, inclusive).map_or(range, |pos| {
+                search_fn(text, ch, range.head, count, inclusive).map_or(range, |pos| {
                     if extend {
                         Range::new(range.anchor, pos)
                     } else {