Strategies take result from previous strategy into account (#4099)

Each strategy takes as candidates the language outputted by the
previous strategy if any. This was already the case for the
Classifier and Heuristic strategies as these couldn't generate new
candidate languages (as opposed to the Modeline, Filename, Shebang,
and Extension strategies).

In practice, this signifies that if, for example, the Shebang
strategy finds two possible languages for a given file (as is
currently possible with the perl interpreter), the next strategy, the
Extension strategy, will use this information and further reduce the
set of possible language.
Currently, without this commit, the Extension strategy would discard
the results from the previous strategy and start anew, possibly
returning a different language from those returned by the Shebang
strategy.

test/fixtures/Perl/01-methods.pl

@@ -0,0 +1,51 @@
+#!perl
+use Test::More;
+use Test::Exception;
+
+use_ok 'Music::ScaleNote';
+
+my $msn = Music::ScaleNote->new(
+    scale_note => 'C',
+    scale_name => 'pminor',
+#    verbose    => 1,
+);
+isa_ok $msn, 'Music::ScaleNote';
+
+my $x;
+
+throws_ok { $x = $msn->get_offset() }
+    qr/note_name, note_format or offset not provided/, 'invalid get_offset';
+
+my $format = 'midinum';
+$x = $msn->get_offset(
+    note_name   => 60,
+    note_format => $format,
+    offset      => 1,
+);
+is $x->format($format), 63, 'get_offset';
+
+$format = 'ISO';
+$x = $msn->get_offset(
+    note_name   => 'D#4',
+    note_format => $format,
+    offset      => -1,
+);
+is $x->format($format), 'C4', 'get_offset';
+
+throws_ok {
+    $x = $msn->get_offset(
+        note_name   => 'C0',
+        note_format => $format,
+        offset      => -1,
+    )
+} qr/Octave: -1 out of bounds/, 'out of bounds';
+
+throws_ok {
+    $x = $msn->get_offset(
+        note_name   => 'A#127',
+        note_format => $format,
+        offset      => 1,
+    )
+} qr/Octave: 128 out of bounds/, 'out of bounds';
+
+done_testing();