binary classifier: detect elixir release-candidate versions (#4851)

The elixir-binary and elixir-library classifiers' regexes only matched
the bare semver triplet (and a single sub-segment for the library), so
release-candidate elixir images were either missed entirely or had
their version truncated:

  $ syft -q elixir:1.12.0-rc | grep elixir   # nothing
  $ syft -q elixir:1.13.0-rc.0 | grep elixir
  elixir   1.13.0   binary                   # truncated, "-rc.0" lost

Extend the version capture group to optionally include
"-<a-z0-9>+(\\.<digits>)?" so "1.12.0-rc.1", "1.13.0-rc.0", etc. match
exactly as the elixir.app and the binary's ELIXIR_VERSION line have
them.

Add a logical fixture under testdata/classifiers/snippets/elixir/
1.12.0-rc.1/linux-amd64 (cloned from the existing 1.19.1 fixture with
just the version strings changed) and register it in
Test_Cataloger_PositiveCases.

Closes #4819

Signed-off-by: Chris (ChrisJr404) <11917633+ChrisJr404@users.noreply.github.com>
Co-authored-by: Chris (ChrisJr404) <11917633+ChrisJr404@users.noreply.github.com>

syft/pkg/cataloger/binary/testdata/classifiers/snippets/elixir/1.12.0-rc.1/linux-amd64/elixir

@@ -0,0 +1,20 @@
+#!/bin/sh
+
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: 2021 The Elixir Team
+# SPDX-FileCopyrightText: 2012 Plataformatec
+
+set -e
+
+ELIXIR_VERSION=1.12.0-rc.1
+
+if [ $# -eq 0 ] || { [ $# -eq 1 ] && { [ "$1" = "--help" ] || [ "$1" = "-h" ]; }; }; then
+  cat <<USAGE >&2
+Usage: $(basename "$0") [options] [.exs file] [data]
+
+## General options
+
+  -e "COMMAND"                 Evaluates the given command (*)
+  -h, --help                   Prints this message (standalone)
+  -r "FILE"                    Requires the given files/patterns (*)
+  -S SCRIPT                    Finds and executes the given script in \$PATH

syft/pkg/cataloger/binary/testdata/classifiers/snippets/elixir/1.12.0-rc.1/linux-amd64/lib/elixir/ebin/elixir.app

@@ -0,0 +1,19 @@
+{application,elixir,
+    [{description,"elixir"},
+     {vsn,"1.12.0-rc.1"},
+     {modules,
+         ['Elixir.Access','Elixir.Agent.Server','Elixir.Agent',
+          'Elixir.Application','Elixir.ArgumentError',
+          elixir_overridable,elixir_parser,elixir_quote,elixir_rewrite,
+          elixir_sup,elixir_tokenizer,elixir_utils,iex]},
+     {registered,[elixir_sup,elixir_config,elixir_code_server]},
+     {applications,[kernel,stdlib,compiler]},
+     {mod,{elixir,[]}},
+     {env,
+         [{ansi_syntax_colors,
+              [{atom,cyan},
+               {binary,default_color},
+               {operator,default_color}]},
+          {check_endianness,true},
+          {dbg_callback,{'Elixir.Macro',dbg,[]}},
+          {time_zone_database,'Elixir.Calendar.UTCOnlyTimeZoneDatabase'}]}]}.