Handle Markdown.LineBreak in LaTeXWriter

Currently LaTeXWriter throws a MethodError when there are LineBreak
nodes in the Markdown AST (i.e. hard linebreak syntax, with \ at EOL).
This patch makes sure we write out \\ in those cases.

CHANGELOG.md

@@ -26,6 +26,7 @@
 ## Version `v0.27.23`
 
 * ![Enhancement][badge-enhancement] The `native` and `docker` PDF builds now run with the `-interaction=batchmode` (instead of `nonstopmode`) and `-halt-on-error` options to make the LaTeX error logs more readable and to fail the build early. ([#1908][github-1908])
+* ![Bugfix][badge-bugfix] The PDF/LaTeX output now handles hard Markdown line breaks (i.e. `Markdown.LineBreak` nodes). ([#1908][github-1908])
 
 ## Version `v0.27.22`
 

src/Writers/LaTeXWriter.jl

@@ -701,6 +701,9 @@ function latexinline(io, hr::Markdown.HorizontalRule)
     _println(io, "\\rule{\\textwidth}{1pt}}")
 end
 
+function latexinline(io, hr::Markdown.LineBreak)
+    _println(io, "\\\\")
+end
 
 # Metadata Nodes get dropped from the final output for every format but are needed throughout
 # rest of the build and so we just leave them in place and print a blank line in their place.

test/examples/src.latex_simple/index.md

@@ -121,3 +121,9 @@ LaTeXEquation2(raw"""
     \end{array}\right]
 """)
 ```
+
+## `LineBreak` node
+
+This sentence\
+should be over **multiple\
+lines**.