EPP Dodger does not respect features

[robertoaloi]

Describe the bug
This is a follow up from #7175, which was partially fixed by #7176.

To Reproduce
Given the following example module (extracted from the OTP 26 highlights post):

-module(t).
-feature(maybe_expr, enable).

-export([listen_port/2]).
listen_port(Port, Options) ->
    maybe
        {ok, ListenSocket} ?= inet_tcp:listen(Port, Options),
        {ok, Address} ?= inet:sockname(ListenSocket),
        {ok, {ListenSocket, Address}}
    end.

The following crashes:

$ erl -enable-feature maybe_expr
> edoc:get_doc("t.erl").
t.erl: at line 7: syntax error before: '{'
t.erl: If the error is caused by too exotic macro
t.erl: definitions or uses of macros, adding option
t.erl: {preprocess, true} can help. See also edoc(3).
** exception exit: error
     in function  edoc:'-check_forms/3-fun-0-'/3 (edoc.erl, line 771)
     in call from lists:foreach_1/2 (lists.erl, line 1686)
     in call from edoc:read_source/2 (edoc.erl, line 640)
     in call from edoc_extract:source/3 (edoc_extract.erl, line 60)

Expected behavior
The function call succeeds.

Affected versions

• OTP 26.0

Additional context
The root cause is in the epp_dodger module, where the io:scan_erl_form/4 function is invoked with an incorrect reserved_word_fun which does not take into account the feature macros, which are currently discarded by the dodger.

A possible solution could be to introduce some state and update the features accordingly, similarly to how the update_feature/4 function works in the epp module. This could be tricky to do in a backward-compatible way, since most of the epp_dodger parsing functions are exported.

Alternatives could be:

• Treat all potential keywords as keywords (would break the opposite case, where the atoms maybe and else
• Use the process dictionary