Fix highlighting for extern crate in doc comments

Author: asuto15

crates/ide/src/syntax_highlighting/highlight.rs

@@ -703,6 +703,7 @@ fn highlight_name_ref_by_syntax(
     };
 
     match parent.kind() {
+        EXTERN_CRATE => HlTag::Symbol(SymbolKind::Module).into(),
         METHOD_CALL_EXPR => ast::MethodCallExpr::cast(parent)
             .and_then(|it| highlight_method_call(sema, krate, &it, edition))
             .unwrap_or_else(|| SymbolKind::Method.into()),

crates/ide/src/syntax_highlighting/test_data/highlight_doctest.html

@@ -50,6 +50,9 @@
 <span class="comment documentation">//!</span><span class="comment documentation"> </span><span class="keyword injected">fn</span><span class="none injected"> </span><span class="function declaration injected">test</span><span class="parenthesis injected">(</span><span class="parenthesis injected">)</span><span class="none injected"> </span><span class="brace injected">{</span><span class="brace injected">}</span>
 <span class="comment documentation">//! ```</span>
 
+<span class="comment documentation">//! ```rust</span>
+<span class="comment documentation">//!</span><span class="comment documentation"> </span><span class="keyword injected">extern</span><span class="none injected"> </span><span class="keyword injected">crate</span><span class="none injected"> </span><span class="module injected">Krate</span><span class="semicolon injected">;</span>
+<span class="comment documentation">//! ```</span>
 <span class="keyword">mod</span> <span class="module declaration">outline_module</span><span class="semicolon">;</span>
 
 <span class="comment documentation">/// ```</span>

crates/ide/src/syntax_highlighting/tests.rs

@@ -722,6 +722,9 @@ fn test_highlight_doc_comment() {
 //! fn test() {}
 //! ```
 
+//! ```rust
+//! extern crate Krate;
+//! ```
 mod outline_module;
 
 /// ```