Make KEY keyword usable as identifier in column and table names

[Copilot]

The KEY keyword was reserved in all contexts, preventing its use as column or table names. This caused parse errors for common schemas where "key" is a natural identifier (e.g., key-value stores, API keys).

Changes

Grammar modifications (src/alasqlparser.jison):

• Added KEY as explicit Literal alternative to allow use as identifier
• Removed standalone KEY Literal variant from IndexKey rule (eliminates parser ambiguity when parsing column definitions)
• Fixed IndexKey to use ColsList for consistency with PrimaryKey/ForeignKey

Test coverage (test/test2203.js):

• 13 test cases validating KEY works as column/table name in SELECT, WHERE, JOIN, GROUP BY, ORDER BY
• Verifies PRIMARY KEY, FOREIGN KEY, UNIQUE KEY syntax unchanged

Example

-- Now works without escaping
CREATE TABLE cache (id INT, key VARCHAR(50), data TEXT);
SELECT * FROM cache WHERE key = 'user:123';

-- Standard SQL KEY constructs still work
CREATE TABLE users (id INT PRIMARY KEY, email VARCHAR(100));
CREATE TABLE items (id INT, FOREIGN KEY (user_id) REFERENCES users(id));

Breaking Change

Index creation via KEY idx_name (column) no longer supported. Use INDEX idx_name (column) instead. This MySQL-specific variant was redundant with the standard INDEX keyword.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Limit the impact of using the keyword: KEY</issue_title>
<issue_description>
Just like in #2203 we want to limit the impact of having keywords. Preferably by making them keywords only in the context needed so the string/word can be used for things like table names and column names i the data - if possible. It might be too much of a hassle to make the impact less, but lets investigate what is possible - still sticking to the SQL-99 specs.

Start by making a test file named test0000.js where 0000 is the issue ID of this ticket. Replicate the use and mimic what usecases could make sense to test, like as a table name, as a column name, as a graph search. Things lke that.

The grammar can be updated in alasqlgrammar.jison. Focus on small precise changes. After updating it we need to run yarn jison && yarn test

Always run yarn format before committing.

</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Limit the impact of using the keyword: KEY #2227

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