Fixing an issue with the function Xml_print.compose_decl.

[Mbodin]

Currently the function Xml_print.compose_decl outputs a literal \n at the end of the first line, instead of a newline character. This makes the generated files invalid.

I also fixed some typos on the way.

[Copilot]

Pull request overview

This PR fixes a critical bug in Xml_print.compose_decl where a literal \n string was being output instead of an actual newline character, which would make generated XML files invalid. The PR also includes several minor typo corrections in comments across the codebase.

Key changes:

• Fixed compose_decl to use character literal '\n' instead of escape sequence in quoted string
• Corrected grammar from "have" to "has" in documentation comments
• Fixed missing space in function call formatting

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 2 comments.

File	Description
lib/xml_print.ml	Fixed literal \n bug by using %c format specifier with '\n' character
lib/svg_sigs.mli	Grammar correction in unary element comment (have → has)
lib/html_sigs.mli	Grammar correction in unary element comment (have → has)
lib/svg_f.ml	Added missing space between function name and argument

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[balat]

Thanks for this, and sorry it waited so long. Picked up in #374, rebased on
master with tests that fail without the fix. I also extended the documentation
comment fix: it read "an element that have exactly one children", so "children"
became "child" too.

Keeping this open until #374 lands, then it closes with it.