The user picker fails when the typed text contains Solr special characters such as the colon of a URL

Problem

Typing a URL, e.g. https://mastodon.example/@alice, in the ActivityPub user picker returns no result and logs a Solr error:

SyntaxError: Cannot parse 'filter(type:webfinger) AND id:*https://mastodon.example/@alice*'

Cause

DefaultActivityPubStorage#searchWebFinger inserts the typed text as is in the Solr filter query filter(type:webfinger) AND id:<query>. The Solr special characters it contains, such as the : of a URL, are not escaped, so the query cannot be parsed.

Suggested fix

Escape the typed text (e.g. with ClientUtils.escapeQueryChars) before inserting it in the query.