SfMaskedEntry (MAUI): Add IsReadOnly mode documentation to Basic-Features.md

[NatarajanSF4844]

Summary

• Introduces documentation for the new IsReadOnly property in .NET MAUI SfMaskedEntry.
• Covers purpose, behavior, API link, XAML/C# examples, runtime toggle, and notes.

What’s included

• New section: “IsReadOnly Mode”
• API reference link to SfMaskedEntry.IsReadOnly

Files changed

• docs/maui/masked-entry/Basic-Features.md (added IsReadOnly section)

API impact

• Property: IsReadOnly (bool), default: false
• No breaking changes; read-only affects only user-initiated edits

Screenshots

• N/A (no image changes required). Add screenshot if desired in a follow-up.

[SyncfusionBuild]

Build Status: INPROGRESS 🔃
Build Location: IsReadOnlyUGDev

[SyncfusionBuild]

CI Status: SUCCESS ✅
Source Compilation: SUCCESS ✅
Build Location: IsReadOnlyUGDev
Technical Error(s): 0
Spelling Error(s): 0
Image Alt Text Error(s): 0
Image Size Error(s): 0
Image Name Error(s): 0
Front matter Error(s): 0
File Path Error(s): 0
CodeSnippet File Path Missing Error(s): 0
Toc Anchor Tags Validation Error(s): 0
MD Tag Validation Error(s): 0