[clang-format] Fix text proto extension scope opening detection

[krasimir]

Summary

This fixes the detection of scope openers in text proto extensions; previously
they were not detected correctly leading to instances like:

msg {
  [aa.bb
] {
key: value
}
}

lib/Format/FormatToken.h

struct FormatToken {
   }
 
   /// \brief Returns \c true if this tokens starts a block-type list, i.e. a
   /// list that should be indented with a block indent.
   bool opensBlockOrBlockTypeList(const FormatStyle &Style) const {
     if (is(TT_TemplateString) && opensScope())
       return true;
     return is(TT_ArrayInitializerLSquare) ||
+           is(TT_ProtoExtensionLSquare) ||
            (is(tok::l_brace) &&
             (BlockKind == BK_Block || is(TT_DictLiteral) ||
              (!Style.Cpp11BracedListStyle && NestingLevel == 0))) ||
            (is(tok::less) && (Style.Language == FormatStyle::LK_Proto ||
                               Style.Language == FormatStyle::LK_TextProto));
   }
 
   /// \brief Returns whether the token is the left square bracket of a C++

unittests/Format/FormatTestTextProto.cpp

verifyFormat("[aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\n"
                "  }\n"
                "}");
   verifyFormat("[aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa/\n"
                " bbbbbbb] {\n"
                "  [type.type] {\n"
                "    keyyyyyyyyyyyyyy: valuuuuuuuuuuuuuuuuuuuuuuuuue\n"
                "  }\n"
                "}");
+  verifyFormat(
+      "aaaaaaaaaaaaaaa {\n"
+      "  bbbbbb {\n"
+      "    [a.b/cy] {\n"
+      "      eeeeeeeeeeeee: \"The lazy coo cat jumps over the lazy hot dog\"\n"
+      "    }\n"
+      "  }\n"
+      "}");
 }
 
 TEST_F(FormatTestTextProto, NoSpaceAfterPercent) {
   verifyFormat("key: %d");
 }
 
 TEST_F(FormatTestTextProto, FormatsRepeatedListInitializers) {
   verifyFormat("keys: []");