TST remove unnecessary exact checks from bundler tests

[Charlie-XIAO]

This PR mainly makes the following changes:

• Removed external_deps and converted part of it into default_deps. The part specifically for external dependencies will be covered in ENH support external dependencies in widget development #66 where the new behavior is implemented.
• Combine replace_apis into default_deps because @deskulpt-test/apis is also a default dependency and the complexity clearly allows to use one test for both of them.
• Skip most error messages in the error chain that does not include useful information, such as load_transformed failed.
• Use regex for error messages that include paths, URLs, etc. This is mainly to reduce complexity.
• Improve output of assert_err_eq a bit to provide more information of what we actually got

[Charlie-XIAO]

We have changed to use regex, so that the + character in the original URL causes problem (well we can just escape that but let's make things simpler).

[github-actions]

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