Multi-query files

[kubukoz]

This PR does waaaaaaay to many things to count, but I'll do my best:

Main features (multi-query files)

• Add support for 0-n use clauses in a file (previously 0-1)
• Add support for 0-n queries in a file (without passing results, as that's out of scope for now) - previously "exactly 1"
• Remove limitation of having either a use clause or an operation-specific service reference (qualified operation name syntax) - the latter takes priority and is required when the service can't be uniquely determined from use clauses alone
• Support completions for queries when the file parses (it didn't make sense before, as the file was limited to just one query anyway)
• Rename code lens to "Run SmithyQL file"

Extra changes

• Disallow running queries in the output panel
• Rewrite some parts of the formatter, making formatting more consistent wrt handling structures vs lists (e.g. the indentation in lists has finally been fixed and looks reasonable)
• Add tests for formatting of each significant piece of syntax, so that all formatting behavior is intentional or at least a known issue
• Improve completions for union members
• Improve completions for queries (a struct is auto-inserted and the cursor is placed inside)
• Optimize LSP<->model conversions by reusing a location map
• Improve parsing errors (e.g. "expected end of string", showing whitespace characters more visibly)
• Tons of internal refactors and improvements for testing and future work.

TODOs (that I know of):

• some end to end tests for the main functionality would be nice to have (even better if they work before this PR)
  • completions
  • diagnostics
  • lens provider
• make compilation work on queries
• a file can be run if it has exactly one query
• a file can be run if it has more queries
• zero queries
• remove "conflicting service references". Prefer what's on the query.
  • support multiple use clauses
  • If all operations in a file have an explicit service attached, we mark the use clause as unused <- moved to Highlight unused / duplicate service clauses #146
  • and provide a code action to remove <- moved to Highlight unused / duplicate service clauses #146
• Add run keyword #150
• "run query" lens aware of multiple queries. I'm not sure how to do this best UX-wise tbh, possibly the lens should go to the first query in the file
• fix completions
• fix document symbols
• fix formatting
• fix resolution error ranges
• validate use clauses for service existence
• move service deprecation notes to the prelude
• fix remaining deprecations/warnings
• clear/issue TODOs added in this PR
• Document language changes for multi-operation files #151

pending bugs:

• failing queries (E.g. connection refused) still don't block subsequent queries from running

[kubukoz]

lgtm xD