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ARROW-7658: [R] Support dplyr filtering on date/time

Building on some notes from @hadley. Reworking the data mask to add in the expression functions, rather than relying on S3 Ops, fixes the issue where Date and POSIXt types couldn't be used in filter expressions.

cc @romainfrancois

Closes #6262 from nealrichardson/dplyr-refactor and squashes the following commits:

1c49ef3bc <Neal Richardson> Test cleanup
f511eecd1 <Neal Richardson> Refactor dplyr filter code to add support for date/time expressions

Authored-by: Neal Richardson <neal.p.richardson@gmail.com>
Signed-off-by: Neal Richardson <neal.p.richardson@gmail.com>