Emacs: Add electric-pair-mode support for triple-quoted strings

[aathn]

This adds support for automatically inserting the closing delimiter for triple-quoted string literals in the Emacs mode.

If erlang-mode and electric-pair-mode are enabled, it works as follows, if | is the cursor position and a double quote is inserted.

""|  ->  """|"""

This is accomplished by adding a function to post-self-insert-hook checking whenever electric-pair-mode is enabled and a third double quote is inserted, and then inserting three more. The approach is taken from python.el, which has the same feature for Python's triple-quote strings.

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CT Test Results

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248 runs  245 ✅ 3 💤 0 ❌

Results for commit 36a35ce.

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[dgud]

Shouldn't we add a newline before closing """ as well?

[IngelaAndin]

@aathn ping

[aathn]

Shouldn't we add a newline before closing """ as well?

We could -- I suppose it's a matter of personal taste. In languages with brace-enclosed blocks { ... }, I'm usually happy to have the closing brace added automatically, but opening the newline myself. Of course, in those languages, it's typically syntactically correct even without the newline, whereas with the triple-quoted string syntax the newline is required

[dgud]

I do think I want that in this case since it is required, I see that as a remainder and education, also it is a new feature
which at least I tend to forget that the newline is required there.

Can you add it please.

[aathn]

Done. Now it works as follows:

""| 
->
"""
|
"""

Does that look okay?

[dgud]

Thanks