Provide consistency for end-of-line chars after 'apio format'.

[zapta]

Currently 'apio format' which uses the verible formatter may leave mixed eol chars in a file and create spurious diff due to eol changes.

This issue is to look into it and provide the user with a clear and documented way to set the eol policy during formatting, using the verible formatter flag or a new apio format flag.

Possible policies may look like:

• No change
• Force LF
• Force CR/LF
• Use the native LF or CR/LF on the underlying system.

Verible formatter usage: https://github.com/chipsalliance/verible/blob/master/verible/verilog/tools/formatter/README.md

Verible formatter flag values
https://github.com/chipsalliance/verible/blob/c1271a00bfb1753a29f37534b4853d9c765eece5/verible/common/formatting/basic-format-style.h#L26

TODO: Add steps to reproduce the problem: formatting on macos, checking in to github, formatting on windows, diff.

[zapta]

The latest version of the Verible formatter has a new option --line_terminator that allows to control the output line terminator though it's broken. Will upgrade to it and retest once it's fix.

Upstream bug report chipsalliance/verible#2463