Make LANGUAGE switchable in runtime (#653)

squashed into a single commit because doing it in steps that all
compiled involved a lot of boilerplate that is pointless to commit to
the repository. GH still has the PR for reference.

g_lang, MAX_MESSAGES_ON_MAP_BOTTOM, and GetLanguagePrefix() were
compile-time constants selected by the ENGLISH/GERMAN/... build
define. They're now runtime, defaulting to the same per-exe value the
define used to pick, and overridable at startup from [Ja2 Settings]
LANGUAGE in Ja2.ini.

-

XMLTacticalMessages is filled at runtime from NewTacticalMessages.xml,
never from compiled-in per-language data: all 8 per-language definitions
were the identical all-zero { L"" }. Delete them and define one shared
buffer in Utils/XML_Language.cpp (the loader) instead of pointer-rebinding
it like the static tables — this drops 9 dead 800KB zero-buffers (8
namespaced copies in LanguageStrings.cpp plus the standalone one) and
leaves no bind-ordering hazard for the XML load path.

-

ExportStrings.cpp privately recompiled one language's full text table
by #including the raw _<LANG>Text.cpp inside namespace Loc, keyed off
the exe-level ENGLISH/GERMAN/... compile macro (whichever the build
happened to select). That's redundant with the pointer globals every
other subsystem already uses (Text.h / LanguageStrings.cpp).

Drop the private copy; the unqualified table names in Loc::ExportStrings
now resolve to the global pointer externs, which BindLanguageStrings has
already rebound to the runtime g_lang by the time this runs (EXPORT_STRINGS
ini flag, checked after GetRuntimeSettings in sgp.cpp). gs_Lang (used only
by Loc::Translate for the Polish/Russian byte remap on raw .edt exports) is
now derived from g_lang via ToLocLanguage, so the export always matches
whatever language is actually active instead of a compile-time pick.

-

Editor/popupmenu.cpp and Strategic/Scheduling.cpp kept their own
call-site extern of gszScheduleActions as CHAR16[NUM_SCHEDULE_ACTIONS][20]
after the real definition changed into a rebindable pointer
(CHAR16 (*)[20], LanguageStrings.cpp). MSVC decays the outer array
dimension when mangling globals, so both declarations produce the same
symbol (?gszScheduleActions@@3PAY0BE@_WA) and the mismatch linked
silently -- but the array-typed TUs then indexed the 4-byte pointer
slot itself as string data, so the editor schedule popup and the map
schedule message text read garbage.

-

add text.def to be single-source of truth on symbol names and use it
 .much simpler, less error prone if adding more strings

-

add pseudo interface for language state. MAX_SAGES_ON_BOTTOM must always
 change in lockstep with g_lang. this isn't foolproof but better

---------

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
Co-authored-by: Claude Sonnet 4.5 <noreply@anthropic.com>

TODO

@@ -2,4 +2,3 @@
 # priority (LOW,HIGH) and description
 
 LOW readd the C4838 (https://learn.microsoft.com/en-us/cpp/error-messages/compiler-warnings/compiler-warning-level-1-c4838) warning to CMakeLists.txt once they're all fixed in the code
-HIGH get rid of ENGLISH, GERMAN, etc preprocessor definitions completely. that way i18n can be built just once and language can be changed in the options screen pending game restart (hotloading will likely require more work)