search: fix symbol match URLs

[bobheadxi]

As reported in #6 . Symbol match URL is a full path, e.g.

/github.com/sourcegraph/sourcegraph@rockskip-symbols/-/blob/enterprise/internal/rockskip/lib.go#L918:6-918:16

The getMatchURL copied from stream.ts gives us most of the same thing, and I was appending this URL to the match URL, creating an invalid URL. I could append this to src.instance instead, but for consistency with content matches which append ?${lineNumber}, I've added a preprocessor to turn url into just the anchor link and append it to the match URL.

Closes #6

Tested:

• single result match, e.g. repo:github.com/sourcegraph/sourcegraph@rockskip-symbols type:symbol queryBlobs
• multi result symbol match, e.g. context:@sourcegrapha/all monitoring type:symbol f:gcp