fix(text_input): ports TG fix to length trim (#15833)

original commit: https://github.com/tgstation/tgstation/pull/81869/commits/df4397565fe6204985bb2b844ee37b5180cee508

local changes: adds new _defines file text.dm to start collecting text specific defines for better code readability

code/__defines/text.dm

@@ -0,0 +1,10 @@
+/**
+ * Holds global defines for use in text input procedures
+ */
+
+
+/**
+ * stuff like `copytext(input, length(input))` will trim the last character of the input,
+ * because DM does it so it copies until the char BEFORE the `end` arg, so we need to bump `end` by 1 in these cases.
+ */
+#define PREVENT_CHARACTER_TRIM_LOSS(integer) (integer + 1)

code/modules/tgui_input/text.dm

@@ -32,9 +32,9 @@
 	if(!user.client.prefs.tgui_input_mode)
 		if(encode)
 			if(multiline)
-				return stripped_multiline_input(user, message, title, default, max_length)
+				return stripped_multiline_input(user, message, title, default, PREVENT_CHARACTER_TRIM_LOSS(max_length))
 			else
-				return stripped_input(user, message, title, default, max_length)
+				return stripped_input(user, message, title, default, PREVENT_CHARACTER_TRIM_LOSS(max_length))
 		else
 			if(multiline)
 				return input(user, message, title, default) as message|null
@@ -159,4 +159,4 @@
 /datum/tgui_input_text/proc/set_entry(entry)
 	if(!isnull(entry))
 		var/converted_entry = encode ? html_encode(entry) : entry
-		src.entry = trim(converted_entry, max_length)
+		src.entry = trim(converted_entry, PREVENT_CHARACTER_TRIM_LOSS(max_length))

vorestation.dme

@@ -96,6 +96,7 @@
 #include "code\__defines\subsystems.dm"
 #include "code\__defines\supply.dm"
 #include "code\__defines\targeting.dm"
+#include "code\__defines\text.dm"
 #include "code\__defines\tgs.config.dm"
 #include "code\__defines\tgs.dm"
 #include "code\__defines\tgui.dm"