Kotlin: Drop support for Kotlin 1.x language versions

Kotlin 2.4.0 no longer supports -language-version 1.9 (the last 1.x
version). Clamp get_language_version() in versions.bzl to minimum 2.0
for extractor builds, and update the supported versions documentation.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

docs/codeql/reusables/supported-versions-compilers.rst

@@ -21,7 +21,7 @@
    Java,"Java 7 to 26 [6]_","javac (OpenJDK and Oracle JDK),
 
    Eclipse compiler for Java (ECJ) [7]_",``.java``
-   Kotlin,"Kotlin 1.8.0 to 2.4.\ *x*","kotlinc",``.kt``
+   Kotlin,"Kotlin 2.0.0 to 2.4.\ *x*","kotlinc",``.kt``
    JavaScript,ECMAScript 2022 or lower,Not applicable,"``.js``, ``.jsx``, ``.mjs``, ``.es``, ``.es6``, ``.htm``, ``.html``, ``.xhtm``, ``.xhtml``, ``.vue``, ``.hbs``, ``.ejs``, ``.njk``, ``.json``, ``.yaml``, ``.yml``, ``.raml``, ``.xml`` [8]_"
    Python [9]_,"2.7, 3.5, 3.6, 3.7, 3.8, 3.9, 3.10, 3.11, 3.12, 3.13",Not applicable,``.py``
    Ruby [10]_,"up to 3.3",Not applicable,"``.rb``, ``.erb``, ``.gemspec``, ``Gemfile``"

java/kotlin-extractor/versions.bzl

@@ -24,6 +24,8 @@ def version_less(lhs, rhs):
 
 def get_language_version(version):
     major, minor, _ = _version_to_tuple(version)
+    if major == 1:
+        return "2.0"
     return "%s.%s" % (major, minor)
 
 def _basename(path):

java/ql/lib/change-notes/2026-06-08-kotlin-drop-1x.md

@@ -0,0 +1,4 @@
+---
+category: deprecation
+---
+* Kotlin versions below 2.0.0 are no longer supported for analysis. The minimum supported version is now Kotlin 2.0.0.