[clang] [lldb] [lldb][TypeSystemClang] Initialize ClassTemplateSpecializationDecl's StrictPackMatch field (PR #126215)

[Pavel Labath via cfe-commits]

labath wrote:

> Cherry picking this onto the 20.x release branch requires #125791 to be cherry-picked first.

But this is just a bugfix for that PR, right? (IOW, if there's no reason to cherry-pick that PR, then there's also no reason cherry-pick this fix)

https://github.com/llvm/llvm-project/pull/126215