Improve VSCode DAP logpoint value summary (#71723)

Currently VSCode logpoint uses `SBValue::GetValue` to get the value for
printing. This is not providing an intuitive result for std::string or
char * -- it shows the pointer value instead of the string content.

This patch improves by prefers `SBValue::GetSummary()` before using
`SBValue::GetValue()`.

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Co-authored-by: jeffreytan81 <jeffreytan@fb.com>