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/function.rs

@@ -1,6 +1,6 @@
 use crate::node::AnyNodeRef;
 use crate::{
-    Arguments, Decorator, Expr, Identifier, Ranged, StmtAsyncFunctionDef, StmtFunctionDef, Suite,
+    Decorator, Expr, Identifier, Parameters, Ranged, StmtAsyncFunctionDef, StmtFunctionDef, Suite,
 };
 use ruff_text_size::TextRange;
 
@@ -49,10 +49,10 @@ impl<'a> AnyFunctionDefinition<'a> {
     }
 
     /// Returns the function arguments (parameters).
-    pub fn arguments(self) -> &'a Arguments {
+    pub fn arguments(self) -> &'a Parameters {
         match self {
-            Self::FunctionDefinition(definition) => definition.args.as_ref(),
-            Self::AsyncFunctionDefinition(definition) => definition.args.as_ref(),
+            Self::FunctionDefinition(definition) => definition.parameters.as_ref(),
+            Self::AsyncFunctionDefinition(definition) => definition.parameters.as_ref(),
         }
     }