Clang: Fix adding completion snippets after {

...e.g. as in "void f() {".

The criteria whether to change snippets got invalidated with

    commit 8d0391a4f9
    Clang: Treat brace initialization as constructor completion

as the completion operator might be T_LBRACE now instead of T_EOF_SYMBOL
for normal completions.

This fixes the plugin test ClangCodeCompletionTest::testCompleteGlobals.

Add also unit tests.

Change-Id: I85cf522b9b307359c5c3e25198dd228cbb68ded0
Reviewed-by: Ivan Donchevskii <ivan.donchevskii@qt.io>

src/plugins/clangcodemodel/clangcompletioncontextanalyzer.h

@@ -58,6 +58,7 @@ public:
     int positionForClang() const { return m_positionForClang; }
     int functionNameStart() const { return m_functionNameStart; }
     int positionEndOfExpression() const { return m_positionEndOfExpression; }
+    bool addSnippets() const { return m_addSnippets; }
 
 private:
     ClangCompletionContextAnalyzer();
@@ -84,6 +85,7 @@ private:
     int m_positionForClang = -1;
     int m_functionNameStart = -1;
     int m_positionEndOfExpression = -1;
+    bool m_addSnippets = false;
 };
 
 } // namespace Internal