Pass FormatContext to NeedsParentheses

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## Summary

I started working on this because I assumed that I would need access to options inside of `NeedsParantheses` but it then turned out that I won't. 
Anyway, it kind of felt nice to pass fewer arguments. So I'm gonna put this out here to get your feedback if you prefer this over passing individual fiels. 

Oh, I sneeked in another change. I renamed `context.contents` to `source`. `contents` is too generic and doesn't tell you anything. 

<!-- What's the purpose of the change? What does it do, and why? -->

## Test Plan

It compiles

crates/ruff_python_formatter/src/statement/stmt_class_def.rs

@@ -79,7 +79,7 @@ impl Format<PyFormatContext<'_>> for FormatInheritanceClause<'_> {
             ..
         } = self.class_definition;
 
-        let source = f.context().contents();
+        let source = f.context().source();
 
         let mut joiner = f.join_comma_separated();
 

crates/ruff_python_formatter/src/statement/stmt_expr.rs

@@ -13,7 +13,7 @@ impl FormatNodeRule<StmtExpr> for FormatStmtExpr {
 
         if let Some(constant) = value.as_constant_expr() {
             if constant.value.is_str()
-                && !is_expression_parenthesized(value.as_ref().into(), f.context().contents())
+                && !is_expression_parenthesized(value.as_ref().into(), f.context().source())
             {
                 return constant.format().with_options(StringLayout::Flat).fmt(f);
             }

crates/ruff_python_formatter/src/statement/stmt_function_def.rs

@@ -56,9 +56,9 @@ impl FormatRule<AnyFunctionDefinition<'_>, PyFormatContext<'_>> for FormatAnyFun
                 // while maintaining the right amount of empty lines between the comment
                 // and the last decorator.
                 let decorator_end =
-                    skip_trailing_trivia(last_decorator.end(), f.context().contents());
+                    skip_trailing_trivia(last_decorator.end(), f.context().source());
 
-                let leading_line = if lines_after(decorator_end, f.context().contents()) <= 1 {
+                let leading_line = if lines_after(decorator_end, f.context().source()) <= 1 {
                     hard_line_break()
                 } else {
                     empty_line()

crates/ruff_python_formatter/src/statement/suite.rs

@@ -43,7 +43,7 @@ impl FormatRule<Suite, PyFormatContext<'_>> for FormatSuite {
         };
 
         let comments = f.context().comments().clone();
-        let source = f.context().contents();
+        let source = f.context().source();
 
         let saved_level = f.context().node_level();
         f.context_mut().set_node_level(node_level);