Cadence 1.0 Banner Breaks External Programs

[jribbink]

Problem

The recently added C1.0 warning that is displayed in the Flow CLI has an unintended consequence of breaking external consumers of the Flow CLI (i.e. Vscode Extension) who parse the output. This banner should be directed to stderr instead to prevent this.

Steps to Reproduce

Try using VSCode Extension with 1.10.0 Flow CLI

Acceptance Criteria

Header goes to stderr

Context

Breaks vscode cadence extension