Fix an error when using regexp with non-encoding option

This PR fixes the following error when using regexp with non-encoding option.

```console
% cat /tmp/example.rb
/\x82/n =~ 'a'

% rubocop -d /tmp/example.rb
(snip)

For /tmp: An error occurred while VariableForce cop was inspecting /tmp/example.rb.
invalid multibyte escape: /\x82/
/Users/koic/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/gems/rubocop-1.25.1/lib/rubocop/cop/variable_force.rb:193:in
`initialize'
/Users/koic/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/gems/rubocop-1.25.1/lib/rubocop/cop/variable_force.rb:193:in `new'
```

This error is due to `VariableForce#regexp_captured_names` not processing the regexp option.
This PR uses `RegexpNode#to_regexp` to prevent the regexp option from being cut.

In addition, the test code replaces the Parser gem (plain) AST with `ProcessedSource#ast`
so that it can call `RegexpNode#to_regexp` defined in the RuboCop AST.

changelog/fix_an_error_when_using_regexp_with_noencoding_option.md

@@ -0,0 +1 @@
+* [#10432](https://github.com/rubocop/rubocop/pull/10432): Fix an error when using regexp with non-encoding option. ([@koic][])

lib/rubocop/cop/variable_force.rb

@@ -186,11 +186,7 @@ def process_regexp_named_captures(node)
       end
 
       def regexp_captured_names(node)
-        regexp_string = node.children.select(&:str_type?).map do |child|
-          child.children.first
-        end.join || ''
-
-        regexp = Regexp.new(regexp_string) # FIXME: Need to be handle `Regexp.new(/\x82/n)`.
+        regexp = node.to_regexp
 
         regexp.named_captures.keys
       end

spec/rubocop/cop/variable_force_spec.rb

@@ -21,7 +21,17 @@
     end
 
     context 'when processing an empty regex' do
-      let(:node) { s(:match_with_lvasgn, s(:regexp, s(:regopt)), s(:str)) }
+      let(:node) { parse_source('// =~ ""').ast }
+
+      it 'does not raise an error' do
+        expect { force.process_node(node) }.not_to raise_error
+      end
+    end
+
+    # FIXME: Remove `broken_on: jruby` when JRuby incompatible is resolved:
+    # https://github.com/jruby/jruby/issues/7113
+    context 'when processing a regex with regopt', broken_on: :jruby do
+      let(:node) { parse_source('/\x82/n =~ "a"').ast }
 
       it 'does not raise an error' do
         expect { force.process_node(node) }.not_to raise_error
@@ -30,13 +40,11 @@
 
     context 'when processing a regexp with a line break at the start of capture parenthesis' do
       let(:node) do
-        s(:match_with_lvasgn,
-          s(:regexp,
-            s(:str, "(\n"),
-            s(:str, "  pattern\n"),
-            s(:str, ')'),
-            s(:regopt)),
-          s(:send, nil?, :string))
+        parse_source(<<~REGEXP).ast
+          /(
+           pattern
+          )/ =~ string
+        REGEXP
       end
 
       it 'does not raise an error' do