Fix edge cases in selective execution

[lihaoyi]

• Fixes handling of private tasks and added tests for that and for renaming tasks. As private tasks and overridden tasks are assigned a .super.xyz suffix during planning, we need to ensure we use the Terminal#render label which includes this suffix rather than the .ctx.segments.render label which does not

• Ensure we preserve all watches during --watch, even if some portion of the build graph was skipped due to selective execution. This ensures that inputs that were skipped can continue to be watched and still trigger downstream changes later

• We should make sure in selective.resolve that we do not call resolve on the outcome of diffMetadata, as that may include private tasks that cannot be resolved externally. Instead we should only call resolve when there is no diff to be had, in which case we need to take the input selector and resolve it to concrete task names to display