feat(tcl): add dynamic argument completion and snippets

The changes add dynamic, semantic argument completion for Tcl
commands and snippet support.

- Introduces DynamicCompletionKind, TclArgumentCompletion, and dynamic rules
  for Tcl to provide variable, procedure, namespace, and path suggestions.
- Adds snippet-backed commands and arguments for Tcl blocks and paths.
- Refactors tcl_argument_completion and updates the LSP to use dynamic path,
  variable, and namespace completions with snippet kinds.

CHANGELOG.md

@@ -4,6 +4,8 @@
 - Add document highlights for procedure and variable occurrences
 - Make completion context-aware and prioritize local, current-file, workspace, and built-in symbols
 - Add command-aware completion for Tcl subcommands, fixed arguments, and valid options
+- Add semantic argument completion for variables, procedures, namespaces, and local file paths
+- Add placeholder-based snippets for common Tcl structures and `dict for`
 - Integrate the NX Tcl Remote Debugger directly into NX Postprocessor Support
 - Add `nx-tcl` attach configurations and breakpoint support for TCL and DEF files
 - Support breakpoints, stepping, stack frames, variables, watches, evaluation, logpoints, hit conditions, and Tcl error stops