Snippet text elements can contain escape sequences
that must be treated properly. Furthermore snippets
must always escape certain characters (like `}`
or `\`). The function has been updated to account
for that. `text` is now also included with
`anything` to match the grammar and can also
match empty text. To avoid infinite loops the
`non-empty` combinator has been added which is
automatically used in the `one_or_more` and
`zero_or more` combinator where the problemn would
occur.
Previously any remaining text of the snippet that could not be parsed
was ignored. This commit adds the `parse_all` function which reports
an error if any text was not consumed by the parser
This refactors the snippet logic to be largely unaware of the rest of
the document. The completion application logic is moved into
generate_transaction_from_snippet which is extended to support
dynamically computing replacement text.
When accepting a snippet completion we automatically delete the
placeholders for now as doing so manual is quite cumbersome. In the
future we should keep these as a mark + virtual text that is
automatically removed once the cursor moves there.
