Fix #2061 indentation with begin/end on the same line.

Indentation is increased on the `\begin` pattern when it is not followed
by the associated `\end` on the same line.

Indentation is decreased on the `\end` pattern but only when it is
located at the beginning of the line, possibly after some spaces.

syntax/syntax.json

@@ -27,8 +27,8 @@
 		["$", "$"]
 	],
 	"indentationRules": {
-		"increaseIndentPattern": "(\\\\begin{(?!document))",
-		"decreaseIndentPattern": "(\\\\end{(?!document))"
+		"increaseIndentPattern": "\\\\begin{(?!document)([a-zA-Z]*)}(?!.*\\\\end{\\1})",
+		"decreaseIndentPattern": "^\\s*\\\\end{(?!document)"
 	},
 	"folding": {
 		"markers": {