Don't lint manual_let_else in cases where the question mark operator would work

Also, lint question_mark for `let...else` clauses that can be simplified to use `?`.
This lint isn't perfect as it doesn't support the unstable try blocks.

tests/ui/manual_let_else_question_mark.fixed

@@ -0,0 +1,56 @@
+//@run-rustfix
+#![allow(unused_braces, unused_variables, dead_code)]
+#![allow(
+    clippy::collapsible_else_if,
+    clippy::unused_unit,
+    clippy::let_unit_value,
+    clippy::match_single_binding,
+    clippy::never_loop
+)]
+#![warn(clippy::manual_let_else, clippy::question_mark)]
+
+enum Variant {
+    A(usize, usize),
+    B(usize),
+    C,
+}
+
+fn g() -> Option<(u8, u8)> {
+    None
+}
+
+fn e() -> Variant {
+    Variant::A(0, 0)
+}
+
+fn main() {}
+
+fn foo() -> Option<()> {
+    // Fire here, normal case
+    let v = g()?;
+
+    // Don't fire here, the pattern is refutable
+    let Variant::A(v, w) = e() else { return None };
+
+    // Fire here, the pattern is irrefutable
+    let (v, w) = g()?;
+
+    // Don't fire manual_let_else in this instance: question mark can be used instead.
+    let v = g()?;
+
+    // Do fire manual_let_else in this instance: question mark cannot be used here due to the return
+    // body.
+    let Some(v) = g() else {
+        return Some(());
+    };
+
+    // Here we could also fire the question_mark lint, but we don't (as it's a match and not an if let).
+    // So we still emit manual_let_else here. For the *resulting* code, we *do* emit the question_mark
+    // lint, so for rustfix reasons, we allow the question_mark lint here.
+    #[allow(clippy::question_mark)]
+    {
+        let Some(v) = g() else { return None };
+    }
+
+    Some(())
+}

tests/ui/manual_let_else_question_mark.rs

@@ -0,0 +1,61 @@
+//@run-rustfix
+#![allow(unused_braces, unused_variables, dead_code)]
+#![allow(
+    clippy::collapsible_else_if,
+    clippy::unused_unit,
+    clippy::let_unit_value,
+    clippy::match_single_binding,
+    clippy::never_loop
+)]
+#![warn(clippy::manual_let_else, clippy::question_mark)]
+
+enum Variant {
+    A(usize, usize),
+    B(usize),
+    C,
+}
+
+fn g() -> Option<(u8, u8)> {
+    None
+}
+
+fn e() -> Variant {
+    Variant::A(0, 0)
+}
+
+fn main() {}
+
+fn foo() -> Option<()> {
+    // Fire here, normal case
+    let Some(v) = g() else { return None };
+
+    // Don't fire here, the pattern is refutable
+    let Variant::A(v, w) = e() else { return None };
+
+    // Fire here, the pattern is irrefutable
+    let Some((v, w)) = g() else { return None };
+
+    // Don't fire manual_let_else in this instance: question mark can be used instead.
+    let v = if let Some(v_some) = g() { v_some } else { return None };
+
+    // Do fire manual_let_else in this instance: question mark cannot be used here due to the return
+    // body.
+    let v = if let Some(v_some) = g() {
+        v_some
+    } else {
+        return Some(());
+    };
+
+    // Here we could also fire the question_mark lint, but we don't (as it's a match and not an if let).
+    // So we still emit manual_let_else here. For the *resulting* code, we *do* emit the question_mark
+    // lint, so for rustfix reasons, we allow the question_mark lint here.
+    #[allow(clippy::question_mark)]
+    {
+        let v = match g() {
+            Some(v_some) => v_some,
+            _ => return None,
+        };
+    }
+
+    Some(())
+}

tests/ui/manual_let_else_question_mark.stderr

@@ -0,0 +1,49 @@
+error: this `let...else` may be rewritten with the `?` operator
+  --> $DIR/manual_let_else_question_mark.rs:30:5
+   |
+LL |     let Some(v) = g() else { return None };
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace it with: `let v = g()?;`
+   |
+   = note: `-D clippy::question-mark` implied by `-D warnings`
+
+error: this `let...else` may be rewritten with the `?` operator
+  --> $DIR/manual_let_else_question_mark.rs:36:5
+   |
+LL |     let Some((v, w)) = g() else { return None };
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace it with: `let (v, w) = g()?;`
+
+error: this block may be rewritten with the `?` operator
+  --> $DIR/manual_let_else_question_mark.rs:39:13
+   |
+LL |     let v = if let Some(v_some) = g() { v_some } else { return None };
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace it with: `g()?`
+
+error: this could be rewritten as `let...else`
+  --> $DIR/manual_let_else_question_mark.rs:43:5
+   |
+LL | /     let v = if let Some(v_some) = g() {
+LL | |         v_some
+LL | |     } else {
+LL | |         return Some(());
+LL | |     };
+   | |______^
+   |
+   = note: `-D clippy::manual-let-else` implied by `-D warnings`
+help: consider writing
+   |
+LL ~     let Some(v) = g() else {
+LL +         return Some(());
+LL +     };
+   |
+
+error: this could be rewritten as `let...else`
+  --> $DIR/manual_let_else_question_mark.rs:54:9
+   |
+LL | /         let v = match g() {
+LL | |             Some(v_some) => v_some,
+LL | |             _ => return None,
+LL | |         };
+   | |__________^ help: consider writing: `let Some(v) = g() else { return None };`
+
+error: aborting due to 5 previous errors
+