Allow terminal accessible view to always preserve cursor position

[meganrogge]

Type of issue

Feature request

Current behavior

terminal.integrated.accessibleViewPreserveCursorPosition preserves the cursor position until new command output arrives, then moves the accessible view to the bottom.

Proposed behavior

Change the setting from a boolean to an enum while preserving the current behavior as the default. Add an option that always preserves the cursor position, including when new command output arrives.

Existing boolean values should continue to map to equivalent behavior for compatibility.