## Description 

This PR fixes addresses some problems with auto-completion:
1. Previously, auto-completion for enum types/variants did not work
inside of match expression. We needed to add both some parsing
resilience to match arm parsing and update the cursor to be able to find
match patterns in the AST. Now we have:


![image](https://github.com/user-attachments/assets/76426e84-59e6-4855-9f20-2ea3135e0483)

2. A smaller update addresses a minor problem with auto-completion after
`{`. Previously, if no intelligent match was found, we were still
returning "default" matches which had an annoying effect of accidentally
auto-completing an essentially random string after any `{` (e.g., the on
starting a function body block).

## Test plan 

All old (updated) and new tests must pass.