Improve error message for missing alternative for conditional expressions.
```
× Expected `:` but found `EOF`
╭─[misc/fail/missing-conditional-alternative-type.ts:2:1]
1 │ type A = 1 extends 2 ? 3
· ┬
· ╰── Conditional starts here
╰────
× Expected `:` but found `EOF`
╭─[misc/fail/missing-conditional-alternative.js:2:1]
1 │ const foo = 1 ? 2
· ┬
· ╰── Conditional starts here
╰────
```
Without this PR, the error mesage is a simple ``Expected `:` but found `EOF` `` only.
sapphi-red