[Tizen][M34-Merge] Implement WebContext::ClearCandidateData

[Tizen][M34-Merge] Implement WebContext::ClearCandidateData

This patch implement ClearCandidateData, which will be
used by ewk_context_form_candidate_data_clear API.
It depended on auto fill feature(TIZEN_AUTOFILL_SUPPORT).
This is code migration from m34 beta to DEV,
Original patch info: http://suprem.sec.samsung.net/gerrit/#/c/4963/

Bug: http://107.108.218.239/bugzilla/show_bug.cgi?id=7742
Reviewed by:  Antonio Gomes

Change-Id: I73795f52d094c2b6f01d7bf5c579ddd60a589f31
Signed-off-by: zhishun.zhou <zhishun.zhou@samsung.com>