feat: renamed headers meta

[jchen042]

Following #988 , the PR is ready for review.

This PR includes:

Added Parser.meta field called renamedHeaders.

• The value is null if the config is headless, or no renamed headers.
• The value is Record<string, string>, in which the keys are the renamed headers and the corresponding values are their original headers, or transformed headers.

The relevant unit tests are updated. I didn't assert all meta in existing unit tests by using assert.deepEqual. Instead, I used assert.deepNestedInclude to assert the values renamedHeaders are correct to avoid a monster PR.

[jchen042]

@mholt @pokoli - can you help merge this PR if everything looks okay? I realised I don't have the permission to do so.

[mholt]

LGTM -- sure. Thanks!