Reduce usage of operator LPCWSTR from CFX_WideString().

This involves adding some explicit c_str() calls. Doing so flagged
PDF_EncodeText() and FindOptionValue() as having suboptimal signatures, in
that we are often throwing away a perfectly fine length and recomputing it.

There are still some platform-specific code that needs the operator.

R=brucedawson@chromium.org

Review URL: https://codereview.chromium.org/1101933003
33 files changed