Implement RFC 23, Part 2 - Plugin pipeline (#1971)

* Implement RFC 23, with the exception of PluginBuilder

* Update documentation.

* Avoid star re-exports.

* Elide implementation details in `Upgradable`.

* Update wording in docs to avoid personal pronouns.

* Update `Upgradable`'s documentation.

* Template the service builder name.

* Template MissingOperationsError directly.

* Code-generate an array directly.

* Sketch out the implementation of `PluginPipeline`.
Remove `PluginExt`.
Add a public constructor for `FilterByOperationName`.

* Ask for a `PluginPipeline` as input for the generated builder.

* Rename `add` to `push`.

* Remove Pluggable.
Rename `composer` module to `pipeline`.

* Remove all mentions of `Pluggable` from docs and examples.

* Fix punctuation.

* Rename variable from `composer` to `pipeline` in doc examples.

* Add a free-standing function for filtering.

* Rename.

* Rename.

* Update design/src/server/anatomy.md

Co-authored-by: david-perez <d@vidp.dev>

* Use `rust` where we do not need templating.

* Remove unused variable.

* Add `expect` message to point users at our issue board in case a panic slips through.

* Typo.

* Update `expect` error message.

* Refactor the `for` loop in ``requestSpecMap` into an `associateWith` call.

* Remove unnecessary bound - since `new` is private, the condition is already enforced via `filter_by_operation_name`.

* Use `Self` in `new`.

* Rename `inner` to `into_inner`

* Rename `concat` to `append` to correctly mirror Vec's API terminology.

* Fix codegen to use renamed method.

* Cut down the public API surface to key methods for a sequence-like interface.

* Add a note about ordering.

* Add method docs.

* Add Default implementation.

* Fix new pokemon bin example.

* Fix new pokemon bin example.

* Fix code-generated builder.

* Fix unresolved symbolProvider.

* Assign the `expect` error message to a variable.

* Do not require a PluginPipeline as input to `builder_with_plugins`.

* Reverse plugin application order.

* Upgrade documentation.

* Add a test to verify that plugin layers are executed in registration order.

* Add license header.

* Update middleware.md

* Typo.

* Fix more builder() calls.

Co-authored-by: david-perez <d@vidp.dev>