Split Constant to individual literal nodes (#8064)

## Summary

This PR splits the `Constant` enum as individual literal nodes. It
introduces the following new nodes for each variant:
* `ExprStringLiteral`
* `ExprBytesLiteral`
* `ExprNumberLiteral`
* `ExprBooleanLiteral`
* `ExprNoneLiteral`
* `ExprEllipsisLiteral`

The main motivation behind this refactor is to introduce the new AST
node for implicit string concatenation in the coming PR. The elements of
that node will be either a string literal, bytes literal or a f-string
which can be implemented using an enum. This means that a string or
bytes literal cannot be represented by `Constant::Str` /
`Constant::Bytes` which creates an inconsistency.

This PR avoids that inconsistency by splitting the constant nodes into
it's own literal nodes, literal being the more appropriate naming
convention from a static analysis tool perspective.

This also makes working with literals in the linter and formatter much
more ergonomic like, for example, if one would want to check if this is
a string literal, it can be done easily using
`Expr::is_string_literal_expr` or matching against `Expr::StringLiteral`
as oppose to matching against the `ExprConstant` and enum `Constant`. A
few AST helper methods can be simplified as well which will be done in a
follow-up PR.

This introduces a new `Expr::is_literal_expr` method which is the same
as `Expr::is_constant_expr`. There are also intermediary changes related
to implicit string concatenation which are quiet less. This is done so
as to avoid having a huge PR which this already is.

## Test Plan

1. Verify and update all of the existing snapshots (parser, visitor)
2. Verify that the ecosystem check output remains **unchanged** for both
the linter and formatter

### Formatter ecosystem check

#### `main`

| project | similarity index | total files | changed files |

|----------------|------------------:|------------------:|------------------:|
| cpython | 0.75803 | 1799 | 1647 |
| django | 0.99983 | 2772 | 34 |
| home-assistant | 0.99953 | 10596 | 186 |
| poetry | 0.99891 | 317 | 17 |
| transformers | 0.99966 | 2657 | 330 |
| twine | 1.00000 | 33 | 0 |
| typeshed | 0.99978 | 3669 | 20 |
| warehouse | 0.99977 | 654 | 13 |
| zulip | 0.99970 | 1459 | 22 |

#### `dhruv/constant-to-literal`

| project | similarity index | total files | changed files |

|----------------|------------------:|------------------:|------------------:|
| cpython | 0.75803 | 1799 | 1647 |
| django | 0.99983 | 2772 | 34 |
| home-assistant | 0.99953 | 10596 | 186 |
| poetry | 0.99891 | 317 | 17 |
| transformers | 0.99966 | 2657 | 330 |
| twine | 1.00000 | 33 | 0 |
| typeshed | 0.99978 | 3669 | 20 |
| warehouse | 0.99977 | 654 | 13 |
| zulip | 0.99970 | 1459 | 22 |

crates/ruff_python_ast/src/visitor/preorder.rs

@@ -1,8 +1,7 @@
 use crate::{
-    Alias, Arguments, BoolOp, CmpOp, Comprehension, Constant, Decorator, ElifElseClause,
-    ExceptHandler, Expr, Keyword, MatchCase, Mod, Operator, Parameter, ParameterWithDefault,
-    Parameters, Pattern, PatternArguments, PatternKeyword, Singleton, Stmt, TypeParam, TypeParams,
-    UnaryOp, WithItem,
+    Alias, Arguments, BoolOp, CmpOp, Comprehension, Decorator, ElifElseClause, ExceptHandler, Expr,
+    Keyword, MatchCase, Mod, Operator, Parameter, ParameterWithDefault, Parameters, Pattern,
+    PatternArguments, PatternKeyword, Singleton, Stmt, TypeParam, TypeParams, UnaryOp, WithItem,
 };
 use crate::{AnyNodeRef, AstNode};
 
@@ -41,9 +40,6 @@ pub trait PreorderVisitor<'a> {
         walk_decorator(self, decorator);
     }
 
-    #[inline]
-    fn visit_constant(&mut self, _constant: &'a Constant) {}
-
     #[inline]
     fn visit_singleton(&mut self, _singleton: &'a Singleton) {}
 
@@ -280,7 +276,12 @@ where
             Expr::Call(expr) => expr.visit_preorder(visitor),
             Expr::FormattedValue(expr) => expr.visit_preorder(visitor),
             Expr::FString(expr) => expr.visit_preorder(visitor),
-            Expr::Constant(expr) => expr.visit_preorder(visitor),
+            Expr::StringLiteral(expr) => expr.visit_preorder(visitor),
+            Expr::BytesLiteral(expr) => expr.visit_preorder(visitor),
+            Expr::NumberLiteral(expr) => expr.visit_preorder(visitor),
+            Expr::BooleanLiteral(expr) => expr.visit_preorder(visitor),
+            Expr::NoneLiteral(expr) => expr.visit_preorder(visitor),
+            Expr::EllipsisLiteral(expr) => expr.visit_preorder(visitor),
             Expr::Attribute(expr) => expr.visit_preorder(visitor),
             Expr::Subscript(expr) => expr.visit_preorder(visitor),
             Expr::Starred(expr) => expr.visit_preorder(visitor),