[6.x] Combine common pdf png functions (#25152)

[stacey-gammon]

backports #25152

• Create common routines for PDF and PNG report processing

• REmove Blacklisted headers not needed

• Changes for issues with PDF and PNG testing

As per Joel Griffith suggestion I added removal of toast notifications after each click download report. And removed setting of image density to 300.

• removed uneccesary image compare routine

• Moved server from property on job to passed in parameter.

• consolidated PDF and PNG testing

Moved test code from PDF and PNG index.test.js into a common index.test.js that now tests the common functions.

• Typescripted the common functions and broke out tests to individual test files

• Create a common create mock server function that all new tests call

• Removed unnecessary exception check and removed test include from index.ts

Summary

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Checklist

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• This was checked for cross-browser compatibility, including a check against IE11
• Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support
• Documentation was added for features that require explanation or tutorials
• Unit or functional tests were updated or added to match the most common scenarios
• This was checked for keyboard-only and screenreader accessibility

For maintainers

• This was checked for breaking API changes and was labeled appropriately
• This includes a feature addition or change that requires a release note and was labeled appropriately

[elasticmachine]

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