Modernize HTML meta tags in org.eclipse.jdt.doc.isv to HTML5 standards

[Copilot]

Addresses HTML5 validation errors in org.eclipse.jdt.doc.isv by removing obsolete meta tags and modernizing charset declarations to HTML5 standards. This is part of the incremental HTML validation cleanup tracked in eclipse-platform#3342.

Changes:

• Removed <meta http-equiv="Content-Style-Type" content="text/css" /> from all 27 HTML files in guide/ directory
• Simplified <meta http-equiv="Content-Type" content="text/html; charset=..." /> to <meta charset="..." /> in all 29 HTML files in guide/ directory (HTML5 standard)
• Verified no white background colors exist in CSS files (already dark-theme compatible)

Example changes:

-<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
-<meta http-equiv="Content-Style-Type" content="text/css" />
+<meta charset="utf-8" />

Technical details:

• The Content-Style-Type meta tag is obsolete in HTML5 and triggers validation warnings. CSS is the implicit default style language in modern browsers.
• The <meta charset="..."> syntax is the HTML5 standard way to declare character encoding, replacing the obsolete http-equiv="Content-Type" syntax.
• All 29 files in the guide folder now comply with HTML5 standards for meta tag declarations.

Original prompt

Fix HTML problems in org.eclipse.jdt.doc.isv

We have a HTML validation that shows a lot of problems reported here:

https://github.com/eclipse-platform/eclipse.platform.releng.aggregator/actions/runs/18816843755/job/53686382833?pr=3342

We want to incrementally fix them for this do:

• select one category of problems (e.g. Bad value "Content-Style-Type" for attribute "http-equiv" on element "meta")
• Fix the problem but do modify more than 20 files at once
• Limit to files in folder org.eclipse.jdt.doc.isv

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[laeubi]

@copilot please also fix the 7 remaining files in the same way.

• also simplify the to meta charset="utf-8 according to html5 standard
• also remove white background colors to allow adaption to dark themes

[Copilot]

@copilot please also fix the 7 remaining files in the same way.

• also simplify the to meta charset="utf-8 according to html5 ...

Done in commit 54bfe4e. Fixed all 7 remaining files by removing Content-Style-Type meta tags, simplified all Content-Type declarations to <meta charset="..."> (HTML5 standard) in all 29 guide files, and verified no white background colors exist in the CSS files (already dark-theme compatible).