Add ability to move to lsp-precise columns

Add ability to move to lsp-precise columns

Also close https://github.com/joaotavora/eglot/issues/125.

Idea and much of design contributed by Michał Krzywkowski
<k.michal@zoho.com>

This introduces the variable eglot-move-to-column-function.

According to the standard, LSP column/character offsets are based
on a count of UTF-16 code units, not actual visual columns.  So
when LSP says position 3 of a line containing just \"aXbc\",
where X is a multi-byte character, it actually means `b', not
`c'.  This is what the function
`eglot-move-to-lsp-abiding-column' does.

However, many servers don't follow the spec this closely, and
thus this variable should be set to `move-to-column' in buffers
managed by those servers.

* eglot.el (eglot-move-to-column-function): New variable.
(eglot-move-to-lsp-abiding-column): New function.
(eglot--lsp-position-to-point): Use eglot-move-to-column-function.

GitHub-reference: fix https://github.com/joaotavora/eglot/issues/124