SERP provider API changes

This document contains changes to the SERP provider API done in versions of Gugal.

Changes in 0.9

SERP providers can now request extra credentials.
- This can be done with the requestCredentials function in ConfigComposable, and should be used if a SERP provider needs more credentials to search than what was initially requested (e.g. an instance of a self-hosted search engine requires a username and password).
A new class, BuildInfo, was added, as a way to access information about the current version of Gugal. (https://gitlab.com/narektor/gugal/-/commit/b7b4048d7892fe4a22137853763826b7858d57fd)
- This API is technically not a part of the SERP provider API, but it's allowed to use it in SERP providers, and it will be kept stable like the SERP provider API is.
Gugal now uses the M3X library for extra UI components.
- Because of this, the com.porg.m3 package is deprecated, and will be removed in a future Gugal version (though not 0.9 or any minor update to it).
  - Most of the deprecated functions can be replaced with the new versions automatically - see Android Studio's tooltip when you hover over the function for details about migration.
A new request type, CustomHeaderJsonRequest, has been added for cases when it's necessary to add headers to requests. (https://gitlab.com/narektor/gugal/-/commit/573453644ec0e353c59551f6e8f648ac0ab0e268)

A special error response, RateLimitedResponse, has been added for cases when a SERP provider is being rate limited.
0.8.2
The com.porg.gugal.Material3* classes have been removed. Please use the alternatives in the com.porg.m3 package. (https://gitlab.com/narektor/gugal/-/commit/642eb7d7ed8df8ee5561004fc369b1f8deab090a)
- As this change is unexpected, please upgrade the Gugal source code to 0.8.1, migrate your config composables to com.porg.m3, then upgrade to 0.8.2.
  Preview 2
The functions in the com.porg.gugal.Material3* classes have been moved to the com.porg.m3 package, and now use a more Compose-style syntax. The Material3* variants are now deprecated and will be removed in 0.9. (https://gitlab.com/narektor/gugal/-/commit/e302e3c313665f1fce0bae8e4fbc4b2b5eae0558)
- Most of the deprecated functions can be replaced with the new versions automatically - see Android Studio's tooltip when you hover over the function for details about migration.

The Result class has been moved to the com.porg.gugal.data package. (https://gitlab.com/narektor/gugal/-/commit/834878522d0ef53769660df4f5f536fa658dcc4d)
Result metadata classes have been added. (https://gitlab.com/narektor/gugal/-/commit/4a1e8253c42122a64a4be4746c19b48858096cc5)
- There are 2 classes:
  - ResultMetadataProduct for products,
  - ResultMetadata as a base class.
- Currently these classes are unsupported.

Added support for search errors in async methods (like Volley's result handler). To make this possible an ErrorResponse class and some overrides for it were added, as well as a new isError argument for search().

Added input validation for ConfigComposable. A SERP provider must enable the Next/Save button of the setup wizard manually by setting ConfigComposable.enableNextButton to true once the input is valid. (https://gitlab.com/narektor/gugal/-/commit/bffe3be2fd08aa5c846634b154d682d7c4fa7206)
Fixed setup loops when the SERP provider doesn't require setup. (https://gitlab.com/narektor/gugal/-/commit/984d1b4e865476d047fb800bdeb2ab924e6e3844)
search() functions that don't return a Volley JsonRequest no longer crash the app. (https://gitlab.com/narektor/gugal/-/commit/347aa0f2cd73dd61ca1c9614fac609cb83259fc3)

The name, description and titleInSearchBox fields in ProviderInfo are no longer strings, and are instead resource IDs pointing to the strings for this SERP provider's name, description and title in the search box. (https://gitlab.com/narektor/gugal/-/commit/541b83b2b608aed842ca01964b970c0886f5bb87)