Instead of lengthy blurbs, switch to single-line, machine-readable
standardized (https://spdx.dev) license identifiers. The Linux kernel
switched long ago, so there is strong precedent.
Three cases are handled: AGPL-only, Apache-only, and dual licensed.
For the latter case, I chose (AGPL-3.0-or-later and Apache-2.0),
reasoning that our changes are extensive enough to apply our license.
The changes we applied mechanically with a script, except to
licenses/README.md.
Closes#9937
As part of changing the codebase to flat_mutation_reader_v2,
change chained_delegating_reader and its user virtual_table.
Since the reader does not process fragments (only forwarding
things around), only glue code is affected. It is also not
performance sensitive, so the extra conversions are unimportant.
Test: unit (dev)
Closes#9706
This change adds a new type of mutation reader which purpose
is to allow inserting operations before an invocation of the proper
reader. It takes a future to wait on and only after it resolves will
it forward the execution to the underlying flat_mutation_reader
implementation.
