Fix DCHECK crashes by Password Manager impl

[mshin-wolvic]

This patch fixes the DCHECK crash caused by the implementation of Passworkd Manager.

• Added WolvicImageDecoder since IdentityManager requires a valid ImageDecoder instance when initializing.
• Nullable Java string should check empty before calling ConvertJavaStringTo{UTF8/UTF16}
• Avoid DCHECK through a fake url of credential since the update status requires the credential info or the saved PasswordForm when adding the new ID/PW via PasswordFormManagerForUI::Update
• Remove AffiliationService to delegate the PasswordForm check in Wolvic Implementations

[mshin-wolvic]

As a general comment we need a better commit description explaining why the DCHECK was hit and how to solve it. With regard to the code I'll trust that the image decoder is correctly implemented in chromium already :)

Updated. Thanks :)