Adjust auto-closing brackets

[lnay]

There were a few conflicts in the auto-closing brackets. In particular, if two opening brackets end with the same character, then the second has no effect. Double/single quotes, and normal brackets "()" are not used in LaTeX syntax. Quotations in prose should be done like `this' or ``that'' but only autoclosing ` is necessary as tapping it twice gives ``''. There are "paired brackets" with multiple characters that appear in LaTeX such as \left{ and \right} in mathmode, or \[ \] for a block equation. However texlab provides snippets for all of these, so that can be used instead and avoid the conflicts mentioned above.

[lnay]

Tested, and all the sensible auto-closing works as expected by either Zed with this config, or by a texlab snippet