Rename Arguments to Parameters in the AST (#6253)

## Summary

This PR renames a few AST nodes for clarity:

- `Arguments` is now `Parameters`
- `Arg` is now `Parameter`
- `ArgWithDefault` is now `ParameterWithDefault`

For now, the attribute names that reference `Parameters` directly are
changed (e.g., on `StmtFunctionDef`), but the attributes on `Parameters`
itself are not (e.g., `vararg`). We may revisit that decision in the
future.

For context, the AST node formerly known as `Arguments` is used in
function definitions. Formally (outside of the Python context),
"arguments" typically refers to "the values passed to a function", while
"parameters" typically refers to "the variables used in a function
definition". E.g., if you Google "arguments vs parameters", you'll get
some explanation like:

> A parameter is a variable in a function definition. It is a
placeholder and hence does not have a concrete value. An argument is a
value passed during function invocation.

We're thus deviating from Python's nomenclature in favor of a scheme
that we find to be more precise.

crates/ruff_python_ast/src/identifier.rs

@@ -10,7 +10,7 @@
 //!
 //! This module can be used to identify the [`TextRange`] of the `except` token.
 
-use crate::{self as ast, Alias, Arg, ArgWithDefault, ExceptHandler, Ranged, Stmt};
+use crate::{self as ast, Alias, ExceptHandler, Parameter, ParameterWithDefault, Ranged, Stmt};
 use ruff_text_size::{TextLen, TextRange, TextSize};
 
 use ruff_python_trivia::{is_python_whitespace, Cursor};
@@ -38,8 +38,8 @@ impl Identifier for Stmt {
     }
 }
 
-impl Identifier for Arg {
-    /// Return the [`TextRange`] for the identifier defining an [`Arg`].
+impl Identifier for Parameter {
+    /// Return the [`TextRange`] for the identifier defining an [`Parameter`].
     ///
     /// For example, return the range of `x` in:
     /// ```python
@@ -51,8 +51,8 @@ impl Identifier for Arg {
     }
 }
 
-impl Identifier for ArgWithDefault {
-    /// Return the [`TextRange`] for the identifier defining an [`ArgWithDefault`].
+impl Identifier for ParameterWithDefault {
+    /// Return the [`TextRange`] for the identifier defining an [`ParameterWithDefault`].
     ///
     /// For example, return the range of `x` in:
     /// ```python