Improve indentation behavior within raw string literals

When editing a C++ raw string literal, e.g. (with `|` denoting the cursor position)

const char* fmt = R"EOF(
This is a raw string literal.|

Pressing enter here gives extra indentation such that the cursor now lies here:

const char* fmt = R"EOF(
This is a raw string literal.
      |

It would be helpful if Qt Creator preserved the indent of the last line seen in the raw string literal, rather than attempting to perform 'smart' indentation (as though this were a continued expression or similar).