Add Ada / SPARK language support via AdaCore Ada Language Server (#1461)

Introduces Language.ADA backed by AdaCore's Ada Language Server (ALS),
the standard LSP-compliant server for Ada — and SPARK, since both share
the .ads/.adb file extensions and ALS distinguishes SPARK by source-level
pragmas/aspects rather than by file type.

ALS is auto-downloaded from AdaCore's GitHub releases (linux-x64/arm64,
darwin-x64/arm64, win32-x64) using the LanguageServerDependencyProviderSinglePath
pattern, with SHA256 verification per-platform. Users can override the
downloaded binary by setting ls_specific_settings.ada.ls_path to a
pre-installed ada_language_server (e.g. from Alire, GNAT Studio, or the
VS Code Ada extension).

Test repo is a minimal multi-file GNAT project (default.gpr, helper.ads,
helper.adb, main.adb). Tests modelled on test_php_basic.py: ls_running,
find_definition (within/across), find_references (within/across),
find_symbol, document_symbols, hierarchical document symbols,
bare-symbol-name sanity check.

docs/01-about/020_programming-languages.md

@@ -28,6 +28,13 @@ or at least freely available for use.
 We currently provide direct, out-of-the-box support for the programming languages listed below.
 Some languages require additional installations or setup steps, as noted.
 
+* **Ada / SPARK**  
+  (uses AdaCore's [Ada Language Server (ALS)](https://github.com/AdaCore/ada_language_server),
+  automatically downloaded; supports `.ads`, `.adb`, and `.ada` files;
+  works best with a `.gpr` GNAT project file at the repository root;
+  SPARK is handled by the same server transparently — set language `ada` for both.
+  To use a pre-installed ALS (e.g. from Alire, GNAT Studio, or the VS Code Ada extension),
+  set `ls_specific_settings.ada.ls_path`.)
 * **AL**
 * **Angular**  
   (experimental; requires Node.js + npm, plus `npm install` having been run in the project root so that `@angular/core`