[ffigen] API docs

[liamappelbe]

• Add missing FFIgen public API docs
• Remove defaultCompilerOpts from the public API. It's superseded by appendCompilerOptions.
• ImportedType should be internal only, as it inherits a lot of internal details from Type, and I want to be able to make arbitrary changes to Type. Added a public ImportedType that mirrors the public API of the internal ImportedType (so this shouldn't be a breaking change). The internal ImportedType wraps the public one and implements Type.
• Change readme relative links to URLs so they work on pub.dev
• Bump example SDK version because the examples use dot shorthands.

Fixes #2590

[github-actions]

PR Health

Breaking changes ✔️

Package	Change	Current Version	New Version	Needed Version	Looking good?

This check can be disabled by tagging the PR with skip-breaking-check.

API leaks ✔️

The following packages contain symbols visible in the public API, but not exported by the library. Export these symbols or remove them from your publicly visible API.

Package	Leaked API symbol	Leaking sources

This check can be disabled by tagging the PR with skip-leaking-check.

Changelog Entry ✔️

Package	Changed Files

Changes to files need to be accounted for in their respective changelogs.

This check can be disabled by tagging the PR with skip-changelog-check.

[codecov]

Codecov Report

❌ Patch coverage is 90.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.88%. Comparing base (f99449e) to head (e766472).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
...ib/src/header_parser/type_extractor/extractor.dart	25.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3707      +/-   ##
==========================================
- Coverage   87.89%   87.88%   -0.01%     
==========================================
  Files         310      310              
  Lines       19771    19787      +16     
==========================================
+ Hits        17377    17390      +13     
- Misses       2394     2397       +3     

Flag	Coverage Δ
ffigen	91.35% <89.65%> (-0.02%)	⬇️
native_pkgs_macos	86.35% <ø> (ø)
native_pkgs_ubuntu	71.98% <ø> (ø)
native_pkgs_windows	75.31% <ø> (ø)
objective_c	63.19% <41.37%> (-0.05%)	⬇️
swiftgen	80.41% <100.00%> (-0.40%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
code_assets	94.96% <ø> (ø)
data_assets	91.56% <ø> (ø)
ffi	100.00% <ø> (ø)
ffigen	91.44% <89.65%> (-0.02%)	⬇️
hooks	86.40% <ø> (ø)
hooks_runner	89.72% <ø> (ø)
jni	66.34% <ø> (ø)
jni_flutter	∅ <ø> (∅)
jni_util	25.00% <ø> (ø)
jnigen	82.85% <ø> (ø)
json_syntax_generator	∅ <ø> (∅)
native_test_helpers	85.71% <ø> (ø)
native_toolchain_c	95.94% <ø> (ø)
objective_c	79.53% <ø> (ø)
pub_formats	∅ <ø> (∅)
record_use	81.48% <ø> (ø)
snippet_tool	66.23% <ø> (ø)
swift2objc	92.95% <ø> (ø)
swiftgen	80.41% <100.00%> (-0.40%)	⬇️
test_case_selector	97.28% <ø> (ø)

Files with missing lines	Coverage Δ
pkgs/ffigen/lib/src/code_generator/imports.dart	91.89% <100.00%> (+1.12%)	⬆️
pkgs/ffigen/lib/src/code_generator/type.dart	87.87% <ø> (ø)
pkgs/ffigen/lib/src/config_provider/config.dart	100.00% <100.00%> (ø)
...s/ffigen/lib/src/config_provider/config_types.dart	84.73% <ø> (ø)
...kgs/ffigen/lib/src/config_provider/public_ast.dart	85.46% <100.00%> (+0.05%)	⬆️
...kgs/ffigen/lib/src/config_provider/spec_utils.dart	70.10% <100.00%> (+0.32%)	⬆️
...gs/ffigen/lib/src/config_provider/yaml_config.dart	91.78% <100.00%> (ø)
pkgs/ffigen/lib/src/ffigen.dart	52.94% <ø> (ø)
pkgs/swiftgen/lib/src/generator.dart	94.64% <100.00%> (-0.19%)	⬇️
...ib/src/header_parser/type_extractor/extractor.dart	91.62% <25.00%> (-1.43%)	⬇️

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[goderbauer]

LGTM