Fixes#22314
Adds expected schema extensions to the tools extension set (if used). Also uses the source config extensions in schema loader instead of temp one, to ensure we can, for example, load a schema.cql with things like `tombstone_gc` or encryption attributes in them.
Bundles together the setup of "always on" schema extensions into a single call, and uses this from the three (3) init points.
Could have opted for static reg via `configurables`, but since we are moving to a single code base, the need for this is going away, hence explicit init seems more in line.
Closesscylladb/scylladb#22327
* github.com:scylladb/scylladb:
tools: Add standard extensions and propagate to schema load
cql_test_env: Use add all extensions instead of inidividually
main: Move extensions adding to function
tomstone_gc: Make validate work for tools
5d63ef4d15