layer.conf: set dotnet 10.0.100 as default preferred version

Add PREFERRED_VERSION_dotnet and PREFERRED_VERSION_dotnet-native
defaulting to 10.0.100 (.NET 10) now that the recipe is available.
Uses weak assignment (?=) so users can override in local.conf.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: Alex J Lennon

conf/layer.conf

@@ -13,6 +13,9 @@ BBFILE_PRIORITY_mono = "5"
 PREFERRED_VERSION_mono ?= "6.12.0.206"
 PREFERRED_VERSION_mono-native ?= "6.12.0.206"
 
+PREFERRED_VERSION_dotnet ?= "10.0.100"
+PREFERRED_VERSION_dotnet-native ?= "10.0.100"
+
 PREFERRED_VERSION_libgdiplus ?= "6.0.5"
 PREFERRED_VERSION_libgdiplus-native ?= "6.0.5"