mssql: fix DML alias targets, byte offsets, dead keyword

Address review findings on the initial engine:

- DELETE dropped its FROM clause, so the T-SQL join form
  (DELETE b FROM books b JOIN ...) failed to resolve. UPDATE and DELETE
  now resolve an alias target against the FROM clause: the matching
  relation becomes the statement's target, and the ON conditions of any
  inner join dissolved by pulling it out move to the WHERE clause.
  Relations under outer joins are left alone.
- AST Location fields carried teesql's UTF-16 code-unit offsets while
  StmtLocation/StmtLen are byte offsets; the converter now maps
  locations through the same byte-offset table as statement spans.
- Drop the unreachable "within group" reserved-keyword case: keywords
  are checked one identifier token at a time.
- Cover INSERT ... OUTPUT and the UPDATE/DELETE alias forms end to end
  under analyze_dml/mssql.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FrnQ4EoZ3WCWWrSsm8bhCP

Author: claude

internal/endtoend/testdata/analyze_dml/mssql/exec.json

@@ -0,0 +1,5 @@
+{
+  "command": "analyze",
+  "args": ["--dialect", "mssql", "--schema", "schema.sql", "query.sql"],
+  "contexts": ["base"]
+}

internal/endtoend/testdata/analyze_dml/mssql/query.sql

@@ -0,0 +1,11 @@
+-- name: CreateAuthor :one
+INSERT INTO authors (name, bio) OUTPUT INSERTED.id VALUES (@name, @bio);
+
+-- name: UpdateAuthorAlias :exec
+UPDATE a SET name = @name FROM authors a WHERE a.id = @id;
+
+-- name: UpdateBookPrices :exec
+UPDATE b SET price = @price FROM books b JOIN authors a ON b.author_id = a.id WHERE a.name = @author;
+
+-- name: DeleteBooksByAuthor :exec
+DELETE b FROM books b INNER JOIN authors a ON b.author_id = a.id WHERE a.name = @name;

internal/endtoend/testdata/analyze_dml/mssql/schema.sql

@@ -0,0 +1,12 @@
+CREATE TABLE authors (
+    id BIGINT IDENTITY(1,1) PRIMARY KEY,
+    name NVARCHAR(100) NOT NULL,
+    bio NVARCHAR(MAX)
+);
+
+CREATE TABLE books (
+    id BIGINT IDENTITY(1,1) PRIMARY KEY,
+    author_id BIGINT NOT NULL,
+    title NVARCHAR(200) NOT NULL,
+    price DECIMAL(10,2)
+);

internal/endtoend/testdata/analyze_dml/mssql/stdout.txt

@@ -0,0 +1,108 @@
+[
+  {
+    "name": "CreateAuthor",
+    "cmd": ":one",
+    "columns": [
+      {
+        "name": "id",
+        "data_type": "bigint",
+        "not_null": true,
+        "is_array": false,
+        "table": "authors"
+      }
+    ],
+    "params": [
+      {
+        "number": 1,
+        "column": {
+          "name": "name",
+          "data_type": "nvarchar",
+          "not_null": true,
+          "is_array": false,
+          "table": "authors"
+        }
+      },
+      {
+        "number": 2,
+        "column": {
+          "name": "bio",
+          "data_type": "nvarchar",
+          "not_null": false,
+          "is_array": false,
+          "table": "authors"
+        }
+      }
+    ]
+  },
+  {
+    "name": "UpdateAuthorAlias",
+    "cmd": ":exec",
+    "columns": [],
+    "params": [
+      {
+        "number": 1,
+        "column": {
+          "name": "name",
+          "data_type": "nvarchar",
+          "not_null": true,
+          "is_array": false,
+          "table": "authors"
+        }
+      },
+      {
+        "number": 2,
+        "column": {
+          "name": "id",
+          "data_type": "bigint",
+          "not_null": true,
+          "is_array": false,
+          "table": "authors"
+        }
+      }
+    ]
+  },
+  {
+    "name": "UpdateBookPrices",
+    "cmd": ":exec",
+    "columns": [],
+    "params": [
+      {
+        "number": 1,
+        "column": {
+          "name": "price",
+          "data_type": "decimal",
+          "not_null": false,
+          "is_array": false,
+          "table": "books"
+        }
+      },
+      {
+        "number": 2,
+        "column": {
+          "name": "name",
+          "data_type": "nvarchar",
+          "not_null": true,
+          "is_array": false,
+          "table": "authors"
+        }
+      }
+    ]
+  },
+  {
+    "name": "DeleteBooksByAuthor",
+    "cmd": ":exec",
+    "columns": [],
+    "params": [
+      {
+        "number": 1,
+        "column": {
+          "name": "name",
+          "data_type": "nvarchar",
+          "not_null": true,
+          "is_array": false,
+          "table": "authors"
+        }
+      }
+    ]
+  }
+]