Suppress Performance/MapMethodChain cop's offenses

This PR suppresses the following `Performance/MapMethodChain` cop's offenses:

```console
$ bundle exec rubocop
(snip)

lib/rubocop/ast/node_pattern/node.rb:210:33: C: Performance/MapMethodChain:
Use map { |x| x.arity_range.minmax } instead of map method chain.
            min, max = children.map(&:arity_range).map(&:minmax).transpose.map(&:sum)
                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
lib/rubocop/ast/node_pattern/node.rb:226:39: C: Performance/MapMethodChain:
Use map { |x| x.arity_range.minmax } instead of map method chain.
            minima, maxima = children.map(&:arity_range).map(&:minmax).transpose
                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
spec/rubocop/ast/node_pattern/lexer_spec.rb:35:21: C: Performance/MapMethodChain:
Use map { |x| x.last.first } instead of map method chain.
      expect(tokens.map(&:last).map(&:first)).to eq \
                    ^^^^^^^^^^^^^^^^^^^^^^^^
spec/rubocop/ast/node_pattern/lexer_spec.rb:71:39: C: Performance/MapMethodChain:
Use map { |x| x.last.first } instead of map method chain.
      zz, percent_zz = tokens.last(2).map(&:last).map(&:first)
                                      ^^^^^^^^^^^^^^^^^^^^^^^^
spec/rubocop/ast/node_pattern/lexer_spec.rb:81:21: C: Performance/MapMethodChain:
Use map { |x| x.last.first } instead of map method chain.
      expect(tokens.map(&:last).map(&:first)).to eq [:&]
                    ^^^^^^^^^^^^^^^^^^^^^^^^

163 files inspected, 5 offenses detected
```

lib/rubocop/ast/node_pattern/node.rb

@@ -207,7 +207,7 @@ class Subsequence < Node
           include ForbidInSeqHead
 
           def arity
-            min, max = children.map(&:arity_range).map(&:minmax).transpose.map(&:sum)
+            min, max = children.map { |child| child.arity_range.minmax }.transpose.map(&:sum)
             min == max ? min || 0 : min..max # NOTE: || 0 for empty case, where min == max == nil.
           end
 
@@ -223,7 +223,7 @@ def in_sequence_head
         # Node class for `{ ... }`
         class Union < Node
           def arity
-            minima, maxima = children.map(&:arity_range).map(&:minmax).transpose
+            minima, maxima = children.map { |child| child.arity_range.minmax }.transpose
             min = minima.min
             max = maxima.max
             min == max ? min : min..max

spec/rubocop/ast/node_pattern/lexer_spec.rb

@@ -32,7 +32,7 @@
     let(:source) { '(array sym $int+ x)' }
 
     it 'is parsed as `$ int + x`' do
-      expect(tokens.map(&:last).map(&:first)).to eq \
+      expect(tokens.map { |token| token.last.first }).to eq \
         %i[( array sym $ int + x )]
     end
   end
@@ -68,7 +68,7 @@
     it 'distinguishes them' do
       types = tokens.map(&:first)
       expect(types).to eq ([:tNODE_TYPE] * 2) + ([:tPARAM_CONST] * 7)
-      zz, percent_zz = tokens.last(2).map(&:last).map(&:first)
+      zz, percent_zz = tokens.last(2).map { |token| token.last.first }
       expect(zz).to eq 'Zz'
       expect(percent_zz).to eq 'Zz'
     end
@@ -78,7 +78,7 @@
     let(:source) { ':&' }
 
     it 'is parsed as `:&`' do
-      expect(tokens.map(&:last).map(&:first)).to eq [:&]
+      expect(tokens.map { |token| token.last.first }).to eq [:&]
     end
   end
 end