DRAFT search: make all filters case insensitive

Created by: attfarhan

Draft so @keegancsmith can comment

early experiment on how to make all the search filters case insensitive, so filters camelCased like repoHasFile would work instead of only lower cased.

From slack:

But I played around more in these files and couldn't get it to work:

https://sourcegraph.com/github.com/sourcegraph/sourcegraph/-/blob/cmd/frontend/internal/pkg/search/query/searchquery.go#L98-108 https://sourcegraph.com/github.com/sourcegraph/sourcegraph/-/blob/cmd/frontend/internal/pkg/search/query/types/check.go#L42-58 https://sourcegraph.com/github.com/sourcegraph/sourcegraph/-/blob/cmd/frontend/internal/pkg/search/query/types/check.go#L88-119

This code in the branch is most likely irrelevant. This is failing in because work needs to be done in the Check part (checkExpr specifically, I believe) of ParseAndCheck