Windows: Fix partial GUI translation due to exhausted translation data pool

The fixed-size data pool used by LoadLanguageData() in
src/Common/Language.c stores the embedded English XML strings plus the
selected language's XML strings. When AddPoolData() returns NULL
because the 1 MB DATA_POOL_CAPACITY is exhausted, LoadLanguageData()
aborts and returns FALSE. The callers ignore the return value, so the
dictionary is left partially populated: later XML entries (many
controls, warnings and newer dialogs) are missing while earlier
entries, including most menu items, remain translated.

Since 1.26.24 the XML language files have grown enough that several
languages now overflow the pool (e.g. Corsican, French, German and
Dutch).

Increase DATA_POOL_CAPACITY in src/Common/Dictionary.h from 1 MB to
4 MB to accommodate current and near-future translations.

This regression only affects the Windows version, which uses the
Win32/C localization path with this fixed pool. Linux and macOS use
wxWidgets/wxTranslations and do not use src/Common/Dictionary.c for
GUI localization.

Fixes: GH-1587

src/Common/Dictionary.h

@@ -19,7 +19,7 @@
 extern "C" {
 #endif
 
-#define DATA_POOL_CAPACITY 1000000
+#define DATA_POOL_CAPACITY 4000000
 
 void AddDictionaryEntry (char *key, int intKey, void *value);
 void *GetDictionaryValue (const char *key);