Consider increasing MAX_FQNAME_LENGTH

When resolving classpath I got the following message:
```
Could not resolve classpath using Cached + (Stdlib + ([] or (((((([] + Maven) + Gradle) + Shell) + Maven) + Gradle) + Shell)) or Backup): Value '/home/..../258-char-long-path/..../....jar' can't be stored to database column because exceeds length (255)"
```

Would it be possible to increase the length of [`MAX_FQNAME_LENGTH`](https://github.com/fwcd/kotlin-language-server/blob/bdba774daa2f4113a723b7a2d07d696be3b563cf/server/src/main/kotlin/org/javacs/kt/index/SymbolIndex.kt#L19) to something larger than 255, for example 511 or 1023? Any negative impact of doing so?

I can open a PR if necessary.

Start in server/src/main/kotlin/org/javacs/kt/index/SymbolIndex.kt at MAX_FQNAME_LENGTH, then trace how the value is stored in the database column. Check the classpath-resolution path that produces the 255-character failure and determine whether increasing the limit avoids it without storage-side problems; done means long classpath values can be stored and resolved successfully.

Written by the indexing model from the issue text.