Add documentation for the pathlib rules (#5815)

Reviving https://github.com/astral-sh/ruff/pull/2348 step by step

Pt 1: docs

Tracking issue: https://github.com/astral-sh/ruff/issues/2646.

crates/ruff/src/rules/flake8_use_pathlib/rules/os_path_getatime.rs

@@ -17,11 +17,15 @@ use ruff_macros::{derive_message_formats, violation};
 ///
 /// ## Examples
 /// ```python
+/// import os
+///
 /// os.path.getsize(__file__)
 /// ```
 ///
 /// Use instead:
 /// ```python
+/// from pathlib import Path
+///
 /// Path(__file__).stat().st_size
 /// ```
 ///

crates/ruff/src/rules/flake8_use_pathlib/rules/os_path_getctime.rs

@@ -17,11 +17,15 @@ use ruff_macros::{derive_message_formats, violation};
 ///
 /// ## Examples
 /// ```python
+/// import os
+///
 /// os.path.getsize(__file__)
 /// ```
 ///
 /// Use instead:
 /// ```python
+/// from pathlib import Path
+///
 /// Path(__file__).stat().st_size
 /// ```
 ///

crates/ruff/src/rules/flake8_use_pathlib/rules/os_path_getmtime.rs

@@ -17,11 +17,15 @@ use ruff_macros::{derive_message_formats, violation};
 ///
 /// ## Examples
 /// ```python
+/// import os
+///
 /// os.path.getsize(__file__)
 /// ```
 ///
 /// Use instead:
 /// ```python
+/// from pathlib import Path
+///
 /// Path(__file__).stat().st_size
 /// ```
 ///

crates/ruff/src/rules/flake8_use_pathlib/rules/os_path_getsize.rs

@@ -17,11 +17,15 @@ use ruff_macros::{derive_message_formats, violation};
 ///
 /// ## Examples
 /// ```python
+/// import os
+///
 /// os.path.getsize(__file__)
 /// ```
 ///
 /// Use instead:
 /// ```python
+/// from pathlib import Path
+///
 /// Path(__file__).stat().st_size
 /// ```
 ///

crates/ruff/src/rules/flake8_use_pathlib/rules/replaceable_by_pathlib.rs

@@ -21,28 +21,50 @@ pub(crate) fn replaceable_by_pathlib(checker: &mut Checker, expr: &Expr) {
             .semantic()
             .resolve_call_path(expr)
             .and_then(|call_path| match call_path.as_slice() {
+                // PTH100
                 ["os", "path", "abspath"] => Some(OsPathAbspath.into()),
+                // PTH101
                 ["os", "chmod"] => Some(OsChmod.into()),
-                ["os", "mkdir"] => Some(OsMkdir.into()),
+                // PTH102
                 ["os", "makedirs"] => Some(OsMakedirs.into()),
+                // PTH103
+                ["os", "mkdir"] => Some(OsMkdir.into()),
+                // PTH104
                 ["os", "rename"] => Some(OsRename.into()),
+                // PTH105
                 ["os", "replace"] => Some(OsReplace.into()),
+                // PTH106
                 ["os", "rmdir"] => Some(OsRmdir.into()),
+                // PTH107
                 ["os", "remove"] => Some(OsRemove.into()),
+                // PTH108
                 ["os", "unlink"] => Some(OsUnlink.into()),
+                // PTH109
                 ["os", "getcwd"] => Some(OsGetcwd.into()),
                 ["os", "getcwdb"] => Some(OsGetcwd.into()),
+                // PTH110
                 ["os", "path", "exists"] => Some(OsPathExists.into()),
+                // PTH111
                 ["os", "path", "expanduser"] => Some(OsPathExpanduser.into()),
+                // PTH112
                 ["os", "path", "isdir"] => Some(OsPathIsdir.into()),
+                // PTH113
                 ["os", "path", "isfile"] => Some(OsPathIsfile.into()),
+                // PTH114
                 ["os", "path", "islink"] => Some(OsPathIslink.into()),
+                // PTH116
                 ["os", "stat"] => Some(OsStat.into()),
+                // PTH117
                 ["os", "path", "isabs"] => Some(OsPathIsabs.into()),
+                // PTH118
                 ["os", "path", "join"] => Some(OsPathJoin.into()),
+                // PTH119
                 ["os", "path", "basename"] => Some(OsPathBasename.into()),
+                // PTH120
                 ["os", "path", "dirname"] => Some(OsPathDirname.into()),
+                // PTH121
                 ["os", "path", "samefile"] => Some(OsPathSamefile.into()),
+                // PTH122
                 ["os", "path", "splitext"] => Some(OsPathSplitext.into()),
                 // PTH202
                 ["os", "path", "getsize"] => Some(OsPathGetsize.into()),
@@ -52,8 +74,11 @@ pub(crate) fn replaceable_by_pathlib(checker: &mut Checker, expr: &Expr) {
                 ["os", "path", "getmtime"] => Some(OsPathGetmtime.into()),
                 // PTH205
                 ["os", "path", "getctime"] => Some(OsPathGetctime.into()),
-                ["", "open"] => Some(BuiltinOpen.into()),
+                // PTH123
+                ["" | "builtin", "open"] => Some(BuiltinOpen.into()),
+                // PTH124
                 ["py", "path", "local"] => Some(PyPath.into()),
+                // PTH115
                 // Python 3.9+
                 ["os", "readlink"] if checker.settings.target_version >= PythonVersion::Py39 => {
                     Some(OsReadlink.into())