fix: better handling of multiple/relative outFiles

[connor4312]

Fixes #1479
Relates to microsoft/vscode#168635

Previously, we naively joined all incoming globs together and ran a
single search for them. However, there are two problems:

• vscode's findTextInFiles doesn't really support multiple globs
• **-prefixed negations, like !**/node_modules/**, should apply
  everywhere, but globbing behavior is to only apply that to the base
  path, which led to confusion (Apply glob negations if glob is navigated outside workspace folder #1479)

This PR redoes the logic. If there are N positive globs, we'll do N
searches in parallel, and apply relevant negations to each one.

[connor4312]

To clarify the 2nd point a little more: while it is correct to only apply the negation to the cwd of the glob evaluation, the directory that js-debug internally uses is pretty opaque to the user, so I think it's a good thing to pretend it's the "filesystem root" effectively and apply it everywhere. If a user wants a more scoped negation, they can just apply that to a specific directory, like !${workspaceFolder}/node_modules/** instead of !**/node_modules/**