Add a fail-closed Tree-sitter PowerShell lowerer (#39213)

## What changed

- Add a Tree-sitter-based lowerer that converts a conservative subset of literal PowerShell commands into argument vectors.
- Reject dynamic expressions, parse recovery, unsupported value conversions, directives, and source outside recognized command nodes instead of guessing their meaning.
- Keep the lowerer alongside the existing production parser for later adoption.

## Testing

- Add fixture-driven coverage for supported literal commands and unsupported or ambiguous syntax, including a dedicated `#requires` rejection test.

GitOrigin-RevId: a6e7acc264ca40df264db4b271e38ae7d89e1ec4

codex-rs/Cargo.lock

@@ -4143,6 +4143,7 @@ dependencies = [
  "shlex",
  "tree-sitter",
  "tree-sitter-bash",
+ "tree-sitter-powershell",
  "url",
  "which 8.0.0",
 ]
@@ -14522,6 +14523,16 @@ version = "0.1.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "009994f150cc0cd50ff54917d5bc8bffe8cad10ca10d81c34da2ec421ae61782"
 
+[[package]]
+name = "tree-sitter-powershell"
+version = "0.26.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3faf304d44b9ddd4a7d97804bb8de7daf564336dd5a526dc6de5b39238243022"
+dependencies = [
+ "cc",
+ "tree-sitter-language",
+]
+
 [[package]]
 name = "tree_magic_mini"
 version = "3.2.2"