Add do snippet, structural snippets, and use-injection dedup (#73)

[JesseHerrick]

Closes #73

• Add "do" to elixirFormSnippets: expands to do..end block with tab stop
  when snippet support is enabled; falls back to plain keyword with
  Preselect when snippet support is off.
• Add structural snippets with parameter slots:
  defmodule, def, defp, defmacro, defmacrop
• Update if snippet to include else clause.
• Add test and describe snippets for ExUnit.
• Add elixirKeywords list: do and end appear as plain keyword completions
  to prevent VS Code from falling back to word-based suggestions.
• Add form-snippet dedup in addCompletionsFromUsing: use-injected
  functions (e.g. ExUnit.Case.test/1) no longer duplicate with their
  form snippet counterpart.

---

Note

Low Risk
Changes are limited to LSP completion insert text and parser token validation for def names; no runtime or security-sensitive paths.

Overview
Improves Dexter LSP completions so Elixir editing in VS Code feels closer to built-in language support: richer snippets, fewer duplicates, and more idiomatic insert text.

Special forms and keywords: elixirFormSnippets now covers structural macros (defmodule, def/defp, defstruct, guards, etc.), adds a do…end snippet, and extends if with an else branch. do and end also appear as plain keyword items (elixirKeywords with Preselect) so Enter does not swap them for word-based suggestions when snippets are off.

Use-chain dedup: When snippet support is on, addCompletionsFromUsing (and import listing) skips functions whose names already have a global form snippet (e.g. Kernel if vs snippet if).

Imported macros: doBlockSnippets (e.g. test, describe, setup) override generic arg-list snippets; noParenFuncs formats ExUnit-style macros as assert expr instead of assert(expr).

Parser: isValidFuncNameToken treats defstruct / defprotocol-style tokens as valid names after defmacro, matching Kernel definitions for indexing.

Tests cover snippets, dedup, do keyword behavior, do-block snippets, and no-paren call style.

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doBlockSnippets ignore definition kind

Medium Severity

applySnippet selects doBlockSnippets using only the function name, so any in-scope completion named test, describe, setup, setup_all, or assert_raise gets an ExUnit-style do/end insert even when the indexed definition is an ordinary def (or a non-macro export), producing invalid or surprising insert text.

 

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