[R] Stop masking base R functions/rethink namespacing

[asfimport]

The package startup message about masking base functions can be scary. We should avoid masking base functions without a compelling reason (i.e. let's do arrow_array() instead of array(), arrow_table()). The arrow versions do very different things than the base functions; plus, end users shouldn’t be dealing directly with Tables and Arrays, so they don’t need to figure so prominently in the public API of the package.

Reporter: Neal Richardson / @nealrichardson
Assignee: Neal Richardson / @nealrichardson

PRs and other links:

• GitHub Pull Request #4491
• GitHub Pull Request #5172
• GitHub Pull Request #5279

_{Note: This issue was originally created as ARROW-5505. Please see the migration documentation for further details.}

[asfimport]

Neal Richardson / @nealrichardson:
PR #4491 aborted pending further design but see the discussion there for ideas.

[asfimport]

Neal Richardson / @nealrichardson:
Issue resolved by pull request 5279
#5279