Add option to use rebar3 fmt instead of standalone erlfmt

[yosida95]

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The current implementation of the fixer for erlfmt, an Erlang code formatter, invokes a standalone erlfmt command. However, the standalone erlfmt command is not distributed by default. Instead, erlfmt is often used as a plugin for Rebar3, the de facto build tool for Erlang.

This patch introduces a new option g:ale_erlang_erlfmt_use_rebar, which is disabled by default, allowing the use of rebar3 fmt instead.

Additionally, this patch fixes a bug that caused the command to read the original source code rather than the stdin.

[yosida95]

@w0rp Thank you for your feedback! I have addressed the points you raised. Could you please review the changes again?

[stale[bot]]

This pull request has been automatically marked as stale because it has not been updated recently. Make sure to write tests and document your changes. See :help ale-dev for information on writing tests. If your pull request is good to merge, bother w0rp or another maintainer again, and get them to merge it.

[w0rp]

I'll close this until it can be reworked and rebased a little. It might make sense to make rebar3 by default, if that makes sense.