vim: monkey-patch html indent

See also: vim/vim#3673

In addition, set as "auto" tags that apply to "content" (as opposed to
e.g. layout, metadata), so that the former can be flush at left margin.

vim/after/indent/html.vim

@@ -0,0 +1,6 @@
+setl inde=FixedHtmlIndent()
+func! FixedHtmlIndent()
+	let indent = HtmlIndent()
+	let b:hi_lasttick = b:changedtick - 1
+	return indent
+endfunc

vim/indent/html.vim

@@ -1,7 +1,12 @@
-let g:html_indent_script1 = 'inc'
-let g:html_indent_style1 = 'inc'
+let g:html_indent_script1 = "inc"
+let g:html_indent_style1 = "inc"
+let g:html_indent_autotags = join(["html","body","article","main","section",
+			\"a","abbr","b","bdi","bdo","cite","code","data","del","dfn","em",
+			\"i","ins","kbd","mark","q","s","ruby","samp","small","span",
+			\"strong","sub","sup","time","u","var","wbr",
+			\"area","keygen","rp","rt","track","wbr","content","shadow"], ",")
+let g:html_indent_inctags = join(["dialog","hgroup","slot"], ",")
 
 setl ts=2
-
 let s:undo = exists("b:undo_indent") ? b:undo_indent . "|" : ""
 let b:undo_indent = s:undo . "setl ts<"