[META] port remaining feeds tamper plugins

This is a meta ticket to port the remaining feeds tamper D7 plugins to this module.

Contributing

Those wishing to contribute to porting the plugins, please create a new issue (if one does not exist) for the plugin you are going to port, assign this to yourself and link the issue to the list of plugins below.

Each plugin will require tests before merging.

Contributors are encouraged to join the feeds meetup on Slack - see the feeds module page for exact times.

Plugins

absolute_url.inc #2976171: Absolute URL Plugin
array_filter.inc
cast_to_int.inc #2960819: Cast to Int Tamper Plugin
convert_boolean.inc #2962792: Plugin: Convert to Boolean
convert_case.inc
copy.inc #2976172: Copy Plugin
country_to_code.inc #2962891: Plugin: Country to Code
default_value.inc #2963016: Plugin: Default Value
encode.inc #2976173: Encode Plugin
efq_finder.inc #2976175: D7 EFQ Finder to D8 Entity finder
explode.inc
find_replace.inc - #2960161: Plugin "Find and replace"
find_replace_regex.inc - #2975179: Find Replace Regex Plugin
hash.inc #2963908: Port hash plugin
html_entity_decode.inc #2960830: Plugin: HTML Entity Decode
html_entity_encode.inc #2960837: Plugin: HTML Entity Encode
implode.inc
keyword_filter.inc #2976176: Keyword Filter Plugin
math.inc #2976177: Math Plugin
number_format.inc #2976179: Number Format Plugin
required.inc - #2937721: Create 'SkipException' classes.
rewrite.inc #2976180: Rewrite Plugin
sprintf.inc #2976182: Sprintf Plugin
state_to_abbrev.inc #2976183: State to Abbrev Plugin
str_pad.inc #2976184: Str Pad
strip_tags.inc #2976186: Strip Tags Plugin
strtotime.inc #2960823: Plugin: Strtotime
timetodate.inc #2976187: Time to Date Plugin
transliteration #3021313: New: Transliteration plugin
trim.inc - #2960790: Plugin: Trim
truncate_text.inc #2976188: Truncate Text Plugin
unique.inc
urldecode.inc #2976189: URL Decode Plugin
urlencode.inc #2976190: URL Encode Plugin