DOC-837 - Add android unsupported details to the mobile page

[kemister85]

Ticket: DOC-837

Site: Staging branch

Changes:

• Added "Android-specific limitations" section to tinymce-for-mobile.adoc
• Documented autocompleter (Emoticons, Charmap, Mentions) limited/non-functional on Android due to GBoard keyboard behavior
• Documented Text Patterns plugin limited functionality on Android
• Added link to release notes 5.1 for additional details
• Fixed broken Text Patterns xref (was textpattern.adoc; corrected to content-behavior-options.adoc#text_patterns)

Prepared for documentation team review.

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Pre-checks:

• Branch is correctly prefixed: hotfix/8/DOC-837
• modules/ROOT/nav.adoc has been updated (if applicable).
• Files have been included where required (if applicable).
• Files removed have been deleted, not just excluded from the build (if applicable).
• Files added for New product features include a release note entry.
• Major or minor version changes have updated the supported-versions.adoc table.
• Build passes without console errors, warnings, or issues.

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Review:

• Documentation Team Lead has reviewed.

[kemister85]

was just a test branch