Code autocomplete: automatically add space after keywords

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# Test case

1. Ask a question
2. SQL
3. Type `sel`
4. Expect autocomplete `select` keyword is an option
5. Press TAB

# Expected outcome

The text `select ` is active in your text editor, including the space after the word select.

# Actual outcome

The text `select` is active in your text editor. You will very likely type SPACE after each time you use this feature.

# Discussion

It is *possible* that the user intends to add a `(` after the `select`, rather than a space, but this is extremely rare.

It is also possible that the user intends to start a new line after autocomplete. Luckily, that situation is easy to correct for:
* If the current line matches `/\s$/` and the user presses RETURN then perform `s/\s$//` before going to the new line.

It is painful to introduce autocorrects that are not what the use intends, perhaps the threshold should be 95% of people want something before an autocorrect is implement. This issue definitely falls into that category.

Start by locating the SQL editor autocomplete implementation and the keyword completion path described in this issue; the payload names no file or test. Verify the change with the `sel` → `select` → Tab flow and confirm the inserted text includes a trailing space without breaking the stated newline case.

Written by the indexing model from the issue text.