[IMM32][SDK] Rename CLIENTIMC_UNKNOWN2 as CLIENTIMC_LOCKED (#8807)

Improve code readability.
JIRA issue: CORE-19268
- Rename CLIENTIMC_UNKNOWN2
  flag as CLIENTIMC_LOCKED.
- Delete unused
  CLIENTIMC_UNKNOWN4 flag.
- Fix the return value of
  Imm32AssignNewLayout function.

sdk/include/reactos/imm32_undoc.h

@@ -170,10 +170,9 @@ C_ASSERT(sizeof(CLIENTIMC) == 0x34);
 /* flags for CLIENTIMC */
 #define CLIENTIMC_WIDE 0x1
 #define CLIENTIMC_ACTIVE 0x2
-#define CLIENTIMC_UNKNOWN4 0x20
 #define CLIENTIMC_DESTROY 0x40
 #define CLIENTIMC_DISABLEIME 0x80
-#define CLIENTIMC_UNKNOWN2 0x100
+#define CLIENTIMC_LOCKED 0x100
 
 PCLIENTIMC WINAPI ImmLockClientImc(_In_ HIMC hImc);
 VOID WINAPI ImmUnlockClientImc(_Inout_ PCLIENTIMC pClientImc);

win32ss/user/imm32/imm.c

@@ -690,9 +690,9 @@ Imm32DestroyInputContext(HIMC hIMC, HKL hKL, BOOL bKeep)
         goto Finish;
     }
 
-    if ((pClientImc->dwFlags & CLIENTIMC_UNKNOWN2) && !bKeep)
+    if ((pClientImc->dwFlags & CLIENTIMC_LOCKED) && !bKeep)
     {
-        ERR("Can't destroy for CLIENTIMC_UNKNOWN2\n");
+        ERR("Can't destroy for CLIENTIMC_LOCKED\n");
         return FALSE;
     }
 
@@ -988,7 +988,7 @@ ImmLockClientImc(_In_ HIMC hImc)
         return NULL;
     }
 
-    pClientImc->dwFlags |= CLIENTIMC_UNKNOWN2;
+    pClientImc->dwFlags |= CLIENTIMC_LOCKED;
 
 Finish:
     InterlockedIncrement(&pClientImc->cLockObj);

win32ss/user/imm32/install.c

@@ -175,7 +175,7 @@ Imm32AssignNewLayout(
         }
     }
 
-    return (HKL)LongToHandle(MAKELONG(wLangID, nID));
+    return UlongToHandle(MAKELONG(wLangID, nID));
 }
 
 static UINT