Better Rust client imports (#3332)

* Better Rust client imports.

* No more "unused_imports" in models for serde_json::Value.
* No more compilation problem for apis requiring serde_json::Value.
* "crate::" prefix for models and apis imports, for compatibility with Rust 2018 edition.

* Rust samples regeneration using new code.

samples/client/petstore/rust/src/models/api_response.rs

@@ -10,9 +10,6 @@
 
 /// ApiResponse : Describes the result of uploading an image resource
 
-#[allow(unused_imports)]
-use serde_json::Value;
-
 
 #[derive(Debug, Serialize, Deserialize)]
 pub struct ApiResponse {

samples/client/petstore/rust/src/models/category.rs

@@ -10,9 +10,6 @@
 
 /// Category : A category for a pet
 
-#[allow(unused_imports)]
-use serde_json::Value;
-
 
 #[derive(Debug, Serialize, Deserialize)]
 pub struct Category {

samples/client/petstore/rust/src/models/order.rs

@@ -10,9 +10,6 @@
 
 /// Order : An order for a pets from the pet store
 
-#[allow(unused_imports)]
-use serde_json::Value;
-
 
 #[derive(Debug, Serialize, Deserialize)]
 pub struct Order {

samples/client/petstore/rust/src/models/pet.rs

@@ -10,22 +10,19 @@
 
 /// Pet : A pet for sale in the pet store
 
-#[allow(unused_imports)]
-use serde_json::Value;
-
 
 #[derive(Debug, Serialize, Deserialize)]
 pub struct Pet {
     #[serde(rename = "id", skip_serializing_if = "Option::is_none")]
     pub id: Option<i64>,
     #[serde(rename = "category", skip_serializing_if = "Option::is_none")]
-    pub category: Option<::models::Category>,
+    pub category: Option<crate::models::Category>,
     #[serde(rename = "name")]
     pub name: String,
     #[serde(rename = "photoUrls")]
     pub photo_urls: Vec<String>,
     #[serde(rename = "tags", skip_serializing_if = "Option::is_none")]
-    pub tags: Option<Vec<::models::Tag>>,
+    pub tags: Option<Vec<crate::models::Tag>>,
     /// pet status in the store
     #[serde(rename = "status", skip_serializing_if = "Option::is_none")]
     pub status: Option<String>,

samples/client/petstore/rust/src/models/tag.rs

@@ -10,9 +10,6 @@
 
 /// Tag : A tag for a pet
 
-#[allow(unused_imports)]
-use serde_json::Value;
-
 
 #[derive(Debug, Serialize, Deserialize)]
 pub struct Tag {

samples/client/petstore/rust/src/models/user.rs

@@ -10,9 +10,6 @@
 
 /// User : A User who is purchasing from the pet store
 
-#[allow(unused_imports)]
-use serde_json::Value;
-
 
 #[derive(Debug, Serialize, Deserialize)]
 pub struct User {