New reference panel: fallback to search-based code intel

Created by: mrnugget

This fixes the first half of https://github.com/sourcegraph/sourcegraph/issues/30970 by renaming the usePreciseCodeIntel hook to useCodeIntel and doing a fallback to search-based code intel when querying precise-code intel yielded no results. This does not yet mix search-based/precise results.

• Uses LanguageSpec definitions copy&pasted from code-intel-extensions
• Determines which Languagespec to use for current document
• Finds token in current document, using LanguageSpec to determine token boundaries and file extensions
• Builds search query to query definitions
• Builds search query to query references
• Tag results as search-based and display that in UI
• Handle clicks on definitions in mini code view correctly
• Filter definitions based on language spec's filterDefinitions

Test plan

• Tested locally by trying out search-based code intel in repositories without precise
• Confirmed that filterDefinition is used by printing comparisons between filtered/unfiltered
• Manually checked graphql queries
• I really want to look into how to best test this as part of #30970 (closed)