longparas: convert GetMaxVisChars from xub_StrLen to sal_Int32

Change-Id: I25fcfc3ae5a599bbd7ebef3071895ec9dbf2949e
longparas: lift 16bit max edit length

Change-Id: Ide74f0a48f06cbe9539f16ef6c6d04bba043dcf9
longparas: unnecessary xub_StrLen cast

Change-Id: I794faf7ba0c2dd32b0c846dd1cf6d1825cf8b63c
longparas: OldTextLen and DeltaStart are unused

Change-Id: Icfcbfece1954675cd4b8882f66726d80b7315e61