Fix XML Beautify indentation after xmlns self-closing element

[alleria173]

Description
The XML Beautify operation produces incorrect indentation for any element that follows a self-closing tag with an xmlns attribute (e.g. <b xmlns="foo" />).

Root cause: vkbeautify's preprocessor splits <b xmlns="foo" /> into two fragments — <b and xmlns="foo" /> — by inserting a delimiter before the xmlns= token. The <b fragment matches the opening-element rule and increments the indentation depth, but the corresponding decrement never fires because the closing /> is on the xmlns fragment rather than a standalone <elm/> token. Every sibling after the self-closing element is therefore indented one level too deep.

The fix moves the xmlns branch before the generic /> branch in the if-else chain, and decrements depth when the xmlns fragment ends with /> (signalling a self-closing element). This restores the correct depth for all subsequent siblings.

Because modifying node_modules/vkbeautify/index.js directly would be overwritten by npm install, the relevant functions have been inlined into XMLBeautify.mjs with the fix applied and the vkbeautify import removed. createShiftArr adds 31 lines (lines 9–39) and the xml formatter xmlBeautify adds 69 lines (lines 41–109). Both carry a JSDoc attribution to the original library: Adapted from vkBeautify (c) 2012 Vadim Kiryukhin, MIT/GPL dual licence.

Existing Issue
Fixes #2501 #2501

Screenshots
N/A — no visual changes.

AI disclosure
Claude Code (claude.ai/code) was used to assist in diagnosing the root cause, implementing the fix, and generating test cases. All code has been reviewed and understood by the submitter.

Test Coverage
A new test file tests/operations/tests/XMLBeautify.mjs has been added with 8 test cases covering baseline behaviour, the two xmlns regression scenarios from the issue, xmlns on non-self-closing tags, multiple xmlns attributes on a single self-closing element, correct indentation of siblings after the fix, XML declarations, and configurable indent strings. All 2064 operation tests pass (npm test).