patch 8.2.4876: MS-Windows: Shift-BS results in strange char in powershell

Problem:    MS-Windows: Shift-BS results in strange character in powershell.
Solution:   Add K_S_BS. (Christian Brabandt, closes #10283, closes #10279)
diff --git a/src/keymap.h b/src/keymap.h
index 85bf7d0..e8832d6 100644
--- a/src/keymap.h
+++ b/src/keymap.h
@@ -276,6 +276,7 @@
     , KE_CANCEL = 102		// return from vgetc()
     , KE_COMMAND = 103		// <Cmd> special key
     , KE_SCRIPT_COMMAND = 104	// <ScriptCmd> special key
+    , KE_S_BS = 105	        // shift + <BS>
 };
 
 /*
@@ -299,6 +300,7 @@
 #define K_C_END		TERMCAP2KEY(KS_EXTRA, KE_C_END)
 #define K_TAB		TERMCAP2KEY(KS_EXTRA, KE_TAB)
 #define K_S_TAB		TERMCAP2KEY('k', 'B')
+#define K_S_BS		TERMCAP2KEY(KS_EXTRA, KE_S_BS)
 
 // extra set of function keys F1-F4, for vt100 compatible xterm
 #define K_XF1		TERMCAP2KEY(KS_EXTRA, KE_XF1)