search docs: update predicate docs to reflect new `repo:has...` syntax

Created by: tbliu98

Stacked on #40765 Part of https://github.com/sourcegraph/sourcegraph/issues/39767

Updates search query docs to reflect the new repo:has... predicate syntax. For now, existing predicates using repo:contains syntax still work.

repo: predicates have been updated:

file: predicates have been updated:

Examples have been updated. Docs on repohasfile and repohascommitafter have been removed as they were already marked as deprecated and the new syntax effectively takes their place.

Test plan

Manually verify docsite updates