Fix ordering between initSentry() and WriteableTmpDir.getInstance().determine()

Fix the Sentry/logging bootstrap ordering so initSentry()'s first getSentryScope() call
can't fire a log write before determine() resolves. Do this through moving the initSentry() call in extension.ts to after `await WriteableTmpDir.getInstance().determine()` and place a comment as to why ("// Logging calls within initSentry() depend on first knowing a writeable tmp dir").

Open extension.ts and inspect the initSentry() call alongside await WriteableTmpDir.getInstance().determine(). Move initSentry() after determine() and add the specified comment; done means determine() completes before initSentry() can log.

Written by the indexing model from the issue text.