Clear auto-import specifier cache when user preferences change

[lsh4711]

Fixes #64820

Registry.specifierCache was only cleared when autoImportSpecifierExcludeRegexes changed, so a change to importModuleSpecifierPreference or importModuleSpecifierEnding kept returning specifiers computed with the old preferences for files that were already open.

This clears the cache on every user preference change instead of comparing the specific preferences that affect specifiers:

• Preference changes only happen when the user edits their settings, so they are rare.
• Clearing is cheap: specifiers are recomputed lazily, only for the imports that are requested afterwards.
• Comparing individual fields is what caused this bug, since importModuleSpecifierPreference and importModuleSpecifierEnding were never added to the check. Clearing unconditionally keeps the cache correct when new preferences that affect specifiers are added later.

Added TestAutoImportModuleSpecifierAfterUserPreferenceChange, which changes autoImportSpecifierExcludeRegexes, importModuleSpecifierEnding and importModuleSpecifierPreference one at a time on an open file and checks the auto-import specifier after each change. The first step covers the existing behavior; the other two fail without this change.

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