Add a floating landscape inset

lib/chkconfig.ltx

@@ -271,6 +271,7 @@
 \TestPackage{a0poster}
 \TestPackage{accents}
 \TestPackage{achicago}
+\TestPackage{afterpage}
 \TestPackage{algorithm}
 \TestPackage{algorithm2e}
 \TestPackage{amsmath}

lib/doc/LaTeXConfig.lyx

@@ -6280,6 +6280,39 @@ literal "false"
 .
 \end_layout
 
+\begin_layout Subsection
+Landscape module
+\end_layout
+
+\begin_layout Subsubsection
+afterpage
+\end_layout
+
+\begin_layout Description
+Found: 
+\begin_inset Info
+type  "package"
+arg   "afterpage"
+\end_inset
+
+
+\end_layout
+
+\begin_layout Description
+CTAN: 
+\family typewriter
+macros/latex/required/tools/
+\end_layout
+
+\begin_layout Description
+Notes: The package 
+\family sans
+afterpage
+\family default
+ provides a command to shift content after the next page break (used for
+ gloating landscape).
+\end_layout
+
 \begin_layout Subsection
 Linguistics module
 \end_layout

lib/layouts/landscape.module

@@ -21,3 +21,12 @@ InsetLayout Flex:Landscape
 	EndFont
 	Requires        lscape
 End
+
+InsetLayout Flex:Landscape_(Floating)
+	CopyStyle	Flex:Landscape
+	LatexType	none
+	LabelString	"Landscape (floating)"
+	LeftDelim	\afterpage{\begin{landscape}<br/>
+	RightDelim	<br/>\end{landscape}}
+	Requires        lscape,afterpage
+End

lib/lyx2lyx/lyx_2_4.py

@@ -170,8 +170,14 @@ def revert_lscape(document):
             i += 1
             continue
 
-        document.body[j - 2 : j + 1] = put_cmd_in_ert("\\end{landscape}")
-        document.body[i : i + 4] = put_cmd_in_ert("\\begin{landscape}")
+        if document.body[i] == "\\begin_inset Flex Landscape (Floating)":
+            document.body[j - 2 : j + 1] = put_cmd_in_ert("\\end{landscape}}")
+            document.body[i : i + 4] = put_cmd_in_ert("\\afterpage{\\begin{landscape}")
+            add_to_preamble(document, ["\\usepackage{afterpage}"])
+        else:
+            document.body[j - 2 : j + 1] = put_cmd_in_ert("\\end{landscape}")
+            document.body[i : i + 4] = put_cmd_in_ert("\\begin{landscape}")
+
         add_to_preamble(document, ["\\usepackage{pdflscape}"])
         # no need to reset i
 

src/LaTeXFeatures.cpp

@@ -971,6 +971,7 @@ char const * simplefeatures[] = {
 	"varwidth",
 	"footnote",
 	"tablefootnote",
+	"afterpage",
 };
 
 char const * bibliofeatures[] = {