toolkit

* Add host Bazel build

Updates target_compatible_with across the repo to ensure that wildcard
builds for both host and rp2040 succeed.

* Get unit tests building

* Add Python script to identify build system differences

Uses the build system tags to make it easier to identify differences
between the CMake and Bazel builds.

* Temporarily disable pico divider test

* Support PICO_BARE_METAL in Bazel

* Support PICO_NO_GC_SECTIONS in Bazel

* Support boot2 configuration in Bazel

Adds support for PICO_DEFAULT_BOOT_STAGE2 and
PICO_DEFAULT_BOOT_STAGE2_FILE in the Bazel build.

* Allowlist some CMake-only options

* Support CXX configuration options in Bazel

* Move multiple_choice_flag.bzl

* Support all pico boards

* Support linking multiple stdio implementations

Changes the Bazel build so stdio implementations are no longer mutually
exclusive.

* Add PICO_BOOT_STAGE2_LINK_IMAGE

* Support PICO_CMSIS_PATH in Bazel

* Support PICO_USE_DEFAULT_MAX_PAGE_SIZE in Bazel

* Silence PICO_CMSIS_VENDOR and PICO_CMSIS_DEVICE differences

* Support PICO_STDIO_USB_CONNECT_WAIT_TIMEOUT_MS in Bazel

* Properly support version defines

* Support embedding binary info in Bazel

* Embed build type in binary

* Support different linker scripts in Bazel build

* Finish out missing PICO_BUILD_DEFINE in Bazel build

* Support PICO_NO_TARGET_NAME

* Reorganize initial configuration options in Bazel

Cleans up and reorganizes some of the initial configuration options
added to the Bazel build so everything is consistent.

* Add builds for pioasm and elf2uf2

* Use Python rules from rules_python

* Actually link in output formats in pioasm tool

* Make tools have public visibility

* Add UF2 Bazel aspect

* Add TODOs for pioasm/uf2 helpers

* Fix compile flag typo

* Update Bazel SDK configuration strings to match recent CMake changes

* Fix pico_divider test

* Clean up straggling TODOs

* Clarify pico_stdio_test compatibility

* Initial Bazel Pico W support

* Add new files from develop

* Clean up compatibility expressions in Bazel build

* Clean up rp2 constraint handling in Bazel

* More Bazel docs cleanup

* Format Bazel build files

* Consolidate transitions in the Pico SDK

* Make every _allowlist_function_transition explicit

* More docs cleanup

* Add a few missing defines

* Improve PICO_CONFIG_HEADER correctness in Bazel

* Minor docs clarifications