move expr_requires_coercion to clippy_utils & some other adjustments

tests/ui/manual_map_option.fixed

@@ -113,7 +113,16 @@ fn main() {
     }
 
     // #6811
-    Some(0).map(|x| vec![x]);
+    match Some(0) {
+        Some(x) => Some(vec![x]),
+        None => None,
+    };
+
+    // Don't lint, coercion
+    let x: Option<Vec<&[u8]>> = match Some(()) {
+        Some(_) => Some(vec![b"1234"]),
+        None => None,
+    };
 
     option_env!("").map(String::from);
 

tests/ui/manual_map_option.rs

@@ -170,6 +170,12 @@ fn main() {
         None => None,
     };
 
+    // Don't lint, coercion
+    let x: Option<Vec<&[u8]>> = match Some(()) {
+        Some(_) => Some(vec![b"1234"]),
+        None => None,
+    };
+
     match option_env!("") {
         Some(x) => Some(String::from(x)),
         None => None,

tests/ui/manual_map_option.stderr

@@ -156,16 +156,7 @@ LL | |     };
    | |_____^ help: try: `Some((String::new(), "test")).as_ref().map(|(x, y)| (y, x))`
 
 error: manual implementation of `Option::map`
-  --> tests/ui/manual_map_option.rs:168:5
-   |
-LL | /     match Some(0) {
-LL | |         Some(x) => Some(vec![x]),
-LL | |         None => None,
-LL | |     };
-   | |_____^ help: try: `Some(0).map(|x| vec![x])`
-
-error: manual implementation of `Option::map`
-  --> tests/ui/manual_map_option.rs:173:5
+  --> tests/ui/manual_map_option.rs:179:5
    |
 LL | /     match option_env!("") {
 LL | |         Some(x) => Some(String::from(x)),
@@ -174,7 +165,7 @@ LL | |     };
    | |_____^ help: try: `option_env!("").map(String::from)`
 
 error: manual implementation of `Option::map`
-  --> tests/ui/manual_map_option.rs:193:12
+  --> tests/ui/manual_map_option.rs:199:12
    |
 LL |       } else if let Some(x) = Some(0) {
    |  ____________^
@@ -185,7 +176,7 @@ LL | |     };
    | |_____^ help: try: `{ Some(0).map(|x| x + 1) }`
 
 error: manual implementation of `Option::map`
-  --> tests/ui/manual_map_option.rs:201:12
+  --> tests/ui/manual_map_option.rs:207:12
    |
 LL |       } else if let Some(x) = Some(0) {
    |  ____________^
@@ -195,5 +186,5 @@ LL | |         None
 LL | |     };
    | |_____^ help: try: `{ Some(0).map(|x| x + 1) }`
 
-error: aborting due to 21 previous errors
+error: aborting due to 20 previous errors