Format import statements (#5493)

## Summary

Format import statements in all their variants. Specifically, this
implemented formatting `StmtImport`, `StmtImportFrom` and `Alias`.

## Test Plan

I added some custom snapshots, even though this has been covered well by
black's tests.

crates/ruff_python_formatter/src/other/alias.rs

@@ -1,5 +1,6 @@
-use crate::{not_yet_implemented, FormatNodeRule, PyFormatter};
-use ruff_formatter::{write, Buffer, FormatResult};
+use crate::{AsFormat, FormatNodeRule, PyFormatter};
+use ruff_formatter::prelude::{space, text};
+use ruff_formatter::{write, Buffer, Format, FormatResult};
 use rustpython_parser::ast::Alias;
 
 #[derive(Default)]
@@ -7,6 +8,15 @@ pub struct FormatAlias;
 
 impl FormatNodeRule<Alias> for FormatAlias {
     fn fmt_fields(&self, item: &Alias, f: &mut PyFormatter) -> FormatResult<()> {
-        write!(f, [not_yet_implemented(item)])
+        let Alias {
+            range: _,
+            name,
+            asname,
+        } = item;
+        name.format().fmt(f)?;
+        if let Some(asname) = asname {
+            write!(f, [space(), text("as"), space(), asname.format()])?;
+        }
+        Ok(())
     }
 }

crates/ruff_python_formatter/src/statement/stmt_import.rs

@@ -1,4 +1,5 @@
-use crate::{not_yet_implemented, FormatNodeRule, PyFormatter};
+use crate::{FormatNodeRule, FormattedIterExt, PyFormatter};
+use ruff_formatter::prelude::{format_args, format_with, space, text};
 use ruff_formatter::{write, Buffer, FormatResult};
 use rustpython_parser::ast::StmtImport;
 
@@ -7,6 +8,12 @@ pub struct FormatStmtImport;
 
 impl FormatNodeRule<StmtImport> for FormatStmtImport {
     fn fmt_fields(&self, item: &StmtImport, f: &mut PyFormatter) -> FormatResult<()> {
-        write!(f, [not_yet_implemented(item)])
+        let StmtImport { names, range: _ } = item;
+        let names = format_with(|f| {
+            f.join_with(&format_args![text(","), space()])
+                .entries(names.iter().formatted())
+                .finish()
+        });
+        write!(f, [text("import"), space(), names])
     }
 }

crates/ruff_python_formatter/src/statement/stmt_import_from.rs

@@ -1,5 +1,7 @@
-use crate::{not_yet_implemented, FormatNodeRule, PyFormatter};
-use ruff_formatter::{write, Buffer, FormatResult};
+use crate::builders::{optional_parentheses, PyFormatterExtensions};
+use crate::{AsFormat, FormatNodeRule, PyFormatter};
+use ruff_formatter::prelude::{dynamic_text, format_with, space, text};
+use ruff_formatter::{write, Buffer, Format, FormatResult};
 use rustpython_parser::ast::StmtImportFrom;
 
 #[derive(Default)]
@@ -7,6 +9,40 @@ pub struct FormatStmtImportFrom;
 
 impl FormatNodeRule<StmtImportFrom> for FormatStmtImportFrom {
     fn fmt_fields(&self, item: &StmtImportFrom, f: &mut PyFormatter) -> FormatResult<()> {
-        write!(f, [not_yet_implemented(item)])
+        let StmtImportFrom {
+            module,
+            names,
+            range: _,
+            level,
+        } = item;
+
+        let level_str = level
+            .map(|level| ".".repeat(level.to_usize()))
+            .unwrap_or(String::default());
+
+        write!(
+            f,
+            [
+                text("from"),
+                space(),
+                dynamic_text(&level_str, None),
+                module.as_ref().map(AsFormat::format),
+                space(),
+                text("import"),
+                space(),
+            ]
+        )?;
+        if let [name] = names.as_slice() {
+            // star can't be surrounded by parentheses
+            if name.name.as_str() == "*" {
+                return text("*").fmt(f);
+            }
+        }
+        let names = format_with(|f| {
+            f.join_comma_separated()
+                .entries(names.iter().map(|name| (name, name.format())))
+                .finish()
+        });
+        optional_parentheses(&names).fmt(f)
     }
 }