string | fill counts clusters, not graphemes; and doesn't count ANSI escape codes (#8134)

Enhancement of new `fill` command (#7846) to handle content including
ANSI escape codes for formatting or multi-code-point Unicode grapheme
clusters.
In both of these cases, the content is (many) bytes longer than its
visible length, and `fill` was counting the extra bytes so not adding
enough fill characters.

# Description

This script:
```rust
# the teacher emoji `\u{1F9D1}\u{200D}\u{1F3EB}` is 3 code points, but only 1 print position wide.
echo "This output should be 3 print positions wide, with leading and trailing `+`"
$"\u{1F9D1}\u{200D}\u{1F3EB}" | fill -c "+" -w 3 -a "c"

echo "This output should be 3 print positions wide, with leading and trailing `+`"
$"(ansi green)a(ansi reset)" | fill -c "+" -w 3 -a c
echo ""
```

Was producing this output:
```rust
This output should be 3 print positions wide, with leading and trailing `+`
🧑‍🏫

This output should be 3 print positions wide, with leading and trailing `+`
a
```

After this PR, it produces this output:
```rust
This output should be 3 print positions wide, with leading and trailing `+`
+🧑‍🏫+

This output should be 3 print positions wide, with leading and trailing `+`
+a+
```
# User-Facing Changes

Users may have to undo fixes they may have introduced to work around the
former behavior. I have one such in my prompt string that I can now
revert.

# Tests + Formatting

Don't forget to add tests that cover your changes.
-- Done

Make sure you've run and fixed any issues with these commands:

- [x] `cargo fmt --all -- --check` to check standard code formatting
(`cargo fmt --all` applies these changes)
- [x] `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A
clippy::needless_collect` to check that you're using the standard code
style
- [x] `cargo test --workspace` to check that all tests pass

# After Submitting

`fill` command not documented in the book, and it still talks about `str
lpad/rpad`. I'll fix.

Note added dependency on a new library `print-positions`, which is an
iterator that yields a complete print position (cluster + Ansi sequence)
per call. Should this be vendored?

Cargo.lock

@@ -2777,6 +2777,7 @@ dependencies = [
  "percent-encoding",
  "polars",
  "powierza-coefficient",
+ "print-positions",
  "proptest",
  "quick-xml 0.27.1",
  "quickcheck",
@@ -3894,6 +3895,15 @@ dependencies = [
  "yansi",
 ]
 
+[[package]]
+name = "print-positions"
+version = "0.6.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1df593470e3ef502e48cb0cfc9a3a61e5f61e967b78e1ed35a67ac615cfbd208"
+dependencies = [
+ "unicode-segmentation",
+]
+
 [[package]]
 name = "proc-macro-error"
 version = "1.0.4"
@@ -5486,9 +5496,9 @@ dependencies = [
 
 [[package]]
 name = "unicode-segmentation"
-version = "1.10.0"
+version = "1.10.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0fdbf052a0783de01e944a6ce7a8cb939e295b1e7be835a1112c3b9a7f047a5a"
+checksum = "1dd624098567895118886609431a7c3b8f516e41d30e0643f03d94592a147e36"
 
 [[package]]
 name = "unicode-width"

Cargo.toml

@@ -77,7 +77,12 @@ signal-hook = { version = "0.3.14", default-features = false }
 winres = "0.1"
 
 [target.'cfg(target_family = "unix")'.dependencies]
-nix = { version = "0.25", default-features = false, features = ["signal", "process", "fs", "term"] }
+nix = { version = "0.25", default-features = false, features = [
+	"signal",
+	"process",
+	"fs",
+	"term",
+] }
 atty = "0.2"
 
 [dev-dependencies]

crates/nu-command/Cargo.toml

@@ -98,6 +98,7 @@ url = "2.2.1"
 uuid = { version = "1.2.2", features = ["v4"] }
 wax = { version = "0.5.0" }
 which = { version = "4.4.0", optional = true }
+print-positions = "0.6.1"
 
 [target.'cfg(windows)'.dependencies]
 winreg = "0.11.0"

crates/nu-command/src/conversions/fill.rs

@@ -5,7 +5,7 @@ use nu_protocol::{
     engine::{Command, EngineState, Stack},
     Category, Example, PipelineData, ShellError, Signature, Span, SyntaxShape, Type, Value,
 };
-use unicode_width::UnicodeWidthStr;
+use print_positions::print_positions;
 
 #[derive(Clone)]
 pub struct Fill;
@@ -225,7 +225,8 @@ fn fill_string(s: &str, args: &Arguments, span: Span) -> Value {
 fn pad(s: &str, width: usize, pad_char: &str, alignment: FillAlignment, truncate: bool) -> String {
     // Attribution: Most of this function was taken from https://github.com/ogham/rust-pad and tweaked. Thank you!
     // Use width instead of len for graphical display
-    let cols = UnicodeWidthStr::width(s);
+
+    let cols = print_positions(s).count();
 
     if cols >= width {
         if truncate {

crates/nu-command/tests/commands/fill.rs

@@ -0,0 +1,33 @@
+use nu_test_support::{nu, pipeline};
+
+#[test]
+fn string_fill_plain() {
+    let actual = nu!(
+        cwd: ".",
+        pipeline(
+            r#"
+            "abc" | fill --alignment center --character "+" --width 5
+            "#
+        )
+    );
+
+    assert_eq!(actual.out, "+abc+");
+}
+
+#[test]
+fn string_fill_fancy() {
+    let actual = nu!(
+        cwd: ".",
+        pipeline(
+            r#"
+            $"(ansi red)a(ansi green)\u{65}\u{308}(ansi cyan)c(ansi reset)" 
+            | fill --alignment center --character "+" --width 5
+            "#
+        )
+    );
+
+    assert_eq!(
+        actual.out,
+        "+\u{1b}[31ma\u{1b}[32me\u{308}\u{1b}[36mc\u{1b}[0m+"
+    );
+}

crates/nu-command/tests/commands/mod.rs

@@ -23,6 +23,7 @@ mod every;
 #[cfg(not(windows))]
 mod exec;
 mod export_def;
+mod fill;
 mod find;
 mod first;
 mod flatten;