Refactor content-type header parsing logic

[mukeshpanchal27]

Trac ticket: https://core.trac.wordpress.org/ticket/43258

Follow-up to #10293

This pull request refines the way the wp_finalize_template_enhancement_output_buffer function parses and checks HTTP headers to determine the content type. The main focus is on making the header parsing more robust and accurate.

Improvements to header parsing:

• Improved parsing of HTTP headers by trimming whitespace and converting the header name to lowercase only (instead of the entire header line), ensuring accurate detection of the Content-Type header.
• Added additional checks to skip malformed headers and continue processing, making the function more resilient to unexpected header formats.

Code cleanup:

• Fixed a minor code indentation issue by removing an unnecessary closing brace.

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This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.

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[westonruter]

Trimming of the header name was intentionally removed in accordance of the HTTP spec

[mukeshpanchal27]

In that case, can we add an inline comment explaining this behaviour so it doesn’t come up again in future reviews? Just curious what’s the reason behind this difference?

[westonruter]

The rationale is in this thread: #10293 (comment)

[westonruter]

I'm not sure this is more refined? Now there are multiple continue statements.

[mukeshpanchal27]

I'm not sure this is more refined? Now there are multiple continue statements.

Is there any drawback to using multiple continue statements?

[westonruter]

It's more verbose, less concise.