Development Patch 1.17.3

Add-ons client

The `forum_auth` attribute now allows authenticating with your forum credentials, as well as no longer requiring the `passphrase` or `email` attributes be populated in the `_server.pbl`. (PR #5866)

Campaigns

Descent into Darkness
- S08: Prevent Spectral Servant from picking up the book (issue #6576)

Northern Rebirth
- S05a_01:
  - Solve units getting stuck in the wall before the spider chamber (issue #6607)
  - Enhance dialogue between Tallin and Abhai (issue #6608)

Sceptre of Fire
- Fixed Thursagan's Arcanister advancement being "lost" after dismounting a minecart (PR #6484).
- Improvements and spelling corrections to the English prose text (PR #6177).

Lua API

New `wesnoth.interface.add_overlay_text` function allows placing arbitrary floating text anywhere on the screen - like `[print]` but with more options (PR #5837).

Terrain

New palisades terrain (^Eqp) and general fence terrain macros cleanup
Rubble pile overlay terrain now connects with adjacent rubble piles
Replace old-style terrain macros (PR #6606)

Translations

Updated translations: British English, Czech, French, Italian

User interface

Map labels are scaled by zoom (PR #6604).
Revamped the Game Load dialog.

Miscellaneous and Bug Fixes

Reduced the size of Isar's Cross map background images.
Resolve crash on systems using musl implementation of libc (issue #6603).
Refactoring of the C++ GUI2 event dispatcher.
Refactoring of the `display` class' theme initialization.
Fixed a crash with "laststrike" (firststrike given to the opponent) weapon specials (issue #6575).
Added more unit tests for weapon specials.