Add option to control overtype of closing pairs

[verte-zerg]

Changes:

• added new option auto-closing-overtype to control overtype of closing pairs (default: true)
• updated documentation

Closes: https://github.com/helix-editor/helix/issues/9595

I've implemented the feature and only then realized that another PR, which is fixing the issue, already exists. However, it looks like there have been no changes for a month.

The PR doesn't break compatibility with old configs.

[dlordi]

Hi, I basically implemented this same solution when I found your PR. Just a couple of differences:

• naming the new option auto-pairs-overtype could help consistency
• swapping the order of tests in next_char == Some(pair.close) && auto_closing_overtype should slightly improve perfomance when this option is off

[verte-zerg]

The PR was rebased (10.03.25)