More consistent modals for “Show JSON”, “Show MD”, whitespace in “Copy”

Summary:
Small diff containing the misc improvements I made while working on D5637.

• If you click "Copy" while viewing a materialization event metadata value, we now preserve whitespace in the original text via innerText (vs textContent)

• The "Show JSON", "Show Markdown", etc. buttons now use a standard modal styling and do not use our custom alert provider, which means that they can appear from within the "View Details" modal without dismissing it.

Test Plan: Run tests

Reviewers: dish

Reviewed By: dish

Differential Revision: https://dagster.phacility.com/D5723