Support expressions starting with var in the evaluator

[HawkForge]

Fixes the bug reported in discussion #4741 (originally #4740). Thanks @kwilson21 for the clear reproduction.

An inline expression that starts with a var declaration, like @input="var v = $event.target.value; if (v.length > 0) { result = 'PASS' }", never runs. The evaluator only wraps an expression in a function body when it starts with if, let or const. Anything else is placed on the right-hand side of an assignment (__self.result = ...), so var throws SyntaxError: Unexpected token 'var'. The error is only logged as a console warning and the handler does nothing.

This adds var to the same check that already handles let and const (#2224). The check appears in three places: the normal evaluator and both branches of the raw evaluator, so all three are updated.

The two new tests in tests/vitest/evaluator.spec.js (evaluate and evaluateRaw with a leading var) fail with the SyntaxError without the change and pass with it. npx vitest run tests/vitest/ passes.

[ekwoka]

....feels like you just shouldn't use var.

[HawkForge]

Agreed, let or const is the better choice, and that already works. The problem is that var is valid JavaScript but fails silently here: the handler does nothing and the only sign is a console warning, which is what confused the reporter in #4741. The change only adds var to the existing let/const check. If you would rather not support it, I am fine closing this.