Clang: Show full completion match first

If prefix is equal to some completion then show it
before anything else.

Task-number: QTCREATORBUG-15445
Change-Id: I976da4a829b818e843d31a76d2818eb5bbedda93
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@qt.io>

src/plugins/texteditor/codeassist/assistproposaliteminterface.h

@@ -47,9 +47,10 @@ public:
     // We compare proposals by enum values, be careful changing their values
     enum class PrefixMatch
     {
-        Exact = 0,
-        Lower = 1,
-        None = 2
+        Full = 0,
+        Exact = 1,
+        Lower = 2,
+        None = 3
     };
 
     AssistProposalItemInterface() = default;