Fix adapter.get_relation to find quoted case-sensitive relations

[prashantpiyush]

resolves dbt-labs/dbt-adapters#694

Problem

The relation matching logic did not consider already
quoted relation path parts.

Solution

This diff updates the relation match logic to use the
same casing for quoted parts.

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX

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[amychen1776]

Thank you @prashantpiyush for opening this up! We will likely review this PR when we tackle this bigger chunk of work to really resolve quoting issues on this adapter at a broader level
dbt-labs/dbt-adapters#704