Move shared Cask examples closer to its clients

In Cask specs, we have recently introduced a couple of specialized
`shared_examples` directories. Those new directories are organized
below their respective packages (for instance,
`cask/artifact/shared_examples` and `cask/cmd/shared_examples`).

This commit moves the rest of the shared examples accordingly.

See also:
https://github.com/Homebrew/brew/pull/5247

Library/Homebrew/test/cask/dsl/caveats_spec.rb

@@ -1,4 +1,4 @@
-require "test/support/helper/spec/shared_examples/cask_dsl_base"
+require "test/cask/dsl/shared_examples/base"
 
 describe Cask::DSL::Caveats, :cask do
   let(:cask) { Cask::CaskLoader.load(cask_path("basic-cask")) }

Library/Homebrew/test/cask/dsl/postflight_spec.rb

@@ -1,5 +1,5 @@
-require "test/support/helper/spec/shared_examples/cask_dsl_base"
-require "test/support/helper/spec/shared_examples/cask_staged"
+require "test/cask/dsl/shared_examples/base"
+require "test/cask/dsl/shared_examples/staged"
 
 describe Cask::DSL::Postflight, :cask do
   let(:cask) { Cask::CaskLoader.load(cask_path("basic-cask")) }

Library/Homebrew/test/cask/dsl/preflight_spec.rb

@@ -1,5 +1,5 @@
-require "test/support/helper/spec/shared_examples/cask_dsl_base"
-require "test/support/helper/spec/shared_examples/cask_staged"
+require "test/cask/dsl/shared_examples/base"
+require "test/cask/dsl/shared_examples/staged"
 
 describe Cask::DSL::Preflight, :cask do
   let(:cask) { Cask::CaskLoader.load(cask_path("basic-cask")) }

Library/Homebrew/test/cask/dsl/uninstall_postflight_spec.rb

@@ -1,4 +1,4 @@
-require "test/support/helper/spec/shared_examples/cask_dsl_base"
+require "test/cask/dsl/shared_examples/base"
 
 describe Cask::DSL::UninstallPostflight, :cask do
   let(:cask) { Cask::CaskLoader.load(cask_path("basic-cask")) }

Library/Homebrew/test/cask/dsl/uninstall_preflight_spec.rb

@@ -1,5 +1,5 @@
-require "test/support/helper/spec/shared_examples/cask_dsl_base"
-require "test/support/helper/spec/shared_examples/cask_staged"
+require "test/cask/dsl/shared_examples/base"
+require "test/cask/dsl/shared_examples/staged"
 
 describe Cask::DSL::UninstallPreflight, :cask do
   let(:cask) { Cask::CaskLoader.load(cask_path("basic-cask")) }