Resolve manual_repeat_n clippy lint

Summary:
```lang=text
warning: this `repeat().take()` can be written more concisely
   --> fbcode/buck2/app/buck2_data/src/lib.rs:122:32
    |
122 |                         .chain(std::iter::repeat('.').take(3))
    |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `repeat_n()` instead: `std::iter::repeat_n('.', 3)`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#manual_repeat_n
    = note: `-W clippy::manual-repeat-n` implied by `-W clippy::all`
    = help: to override `-W clippy::all` add `#[allow(clippy::manual_repeat_n)]`

warning: this `repeat().take()` can be written more concisely
   --> fbcode/buck2/superconsole/src/content/lines.rs:248:24
    |
248 |         let extender = iter::repeat(Line::default()).take(amount);
    |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `repeat_n()` instead: `std::iter::repeat_n(Line::default(), amount)`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#manual_repeat_n
    = note: `-W clippy::manual-repeat-n` implied by `-W clippy::all`
    = help: to override `-W clippy::all` add `#[allow(clippy::manual_repeat_n)]`

warning: this `repeat().take()` can be written more concisely
   --> fbcode/buck2/superconsole/src/content/lines.rs:254:24
    |
254 |         let extender = iter::repeat(Line::default()).take(amount);
    |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `repeat_n()` instead: `std::iter::repeat_n(Line::default(), amount)`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#manual_repeat_n

warning: this `repeat().take()` can be written more concisely
   --> fbcode/buck2/superconsole/src/components/splitting.rs:355:27
    |
355 |             output.extend(iter::repeat(Line::default()).take(8));
    |                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `repeat_n()` instead: `std::iter::repeat_n(Line::default(), 8)`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#manual_repeat_n
    = note: `-W clippy::manual-repeat-n` implied by `-W clippy::all`
    = help: to override `-W clippy::all` add `#[allow(clippy::manual_repeat_n)]`

warning: this `repeat().take()` can be written more concisely
   --> fbcode/buck2/superconsole/src/components/splitting.rs:357:27
    |
357 |             output.extend(iter::repeat(Line::default()).take(7));
    |                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `repeat_n()` instead: `std::iter::repeat_n(Line::default(), 7)`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#manual_repeat_n

warning: this `repeat().take()` can be written more concisely
   --> fbcode/buck2/superconsole/src/content/lines.rs:248:24
    |
248 |         let extender = iter::repeat(Line::default()).take(amount);
    |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `repeat_n()` instead: `std::iter::repeat_n(Line::default(), amount)`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#manual_repeat_n

errors: 0; warnings: 6
```

Reviewed By: diliop

Differential Revision: D72737417

fbshipit-source-id: 133332287e92073c7bf6695bf06ec6a51a8ee1d7

Author: David Tolnay

src/components/splitting.rs

@@ -352,9 +352,9 @@ mod tests {
             );
 
             let mut output = top;
-            output.extend(iter::repeat(Line::default()).take(8));
+            output.extend(iter::repeat_n(Line::default(), 8));
             output.extend(bottom);
-            output.extend(iter::repeat(Line::default()).take(7));
+            output.extend(iter::repeat_n(Line::default(), 7));
 
             let drawn = splitter
                 .draw(Dimensions::new(20, 20), DrawMode::Normal)

src/content/lines.rs

@@ -245,13 +245,13 @@ impl Lines {
 
     /// Extends the Lines list by the given length, adding empty lines at the bottom
     pub fn pad_lines_bottom(&mut self, amount: usize) {
-        let extender = iter::repeat(Line::default()).take(amount);
+        let extender = iter::repeat_n(Line::default(), amount);
         self.extend(extender);
     }
 
     /// Same functionality as `pad_lines_bottom` but on the top.
     pub fn pad_lines_top(&mut self, amount: usize) {
-        let extender = iter::repeat(Line::default()).take(amount);
+        let extender = iter::repeat_n(Line::default(), amount);
 
         self.0.splice(0..0, extender);
     }