Implement `@pattern` on `string` shapes (#1998)

* Refactor `ConstrainedStringGenerator` to extract length checking

* Extract `TryFrom` rendering into its own function

* Extract `ConstraintViolation` definition to separate function

* Add pattern check mock for `@pattern` trait

* Add `regex` to list of server dependencies

* Use real regex check in `check_pattern`

* Add `@pattern` to traits that make `string` shapes directly constrained

* Remove unsupported validation for `@pattern` on strings

* Fix test cases in `ConstraintsTest`

* Remove test disallowing `@pattern` on strings

* Add first test case for `@pattern` on strings

* Fix codegen in `ConstraintViolation::as_validation_exception_field`

* Use `OnceCell` to store `@pattern`'s regex

* Tidy up `ConstrainedStringGenerator` to work with many constraints

* Rename `handleTrait` -> `fromTrait` and make it a static method

* Add docs for `ConstraintViolation` variants

* Fix unescaped slashes in regexes

* Quick hack to get tests compiling

* Fix `sensitive_string_display_implementation` test

* Use new fn name: `asType` -> `toType`

* Refactor `ConstrainedStringGenerator` to not pass in `constraints`

* Add `@pattern` test

* Use `Lazy` instead of `OnceCell`

* Store `&'static str` in `Pattern` error instead of `String`

* Move `TraitInfo` to the bottom

* Extract branches in `TraitInfo.fromTrait` into separate functions

* Add `PatternTrait.validationErrorMessage`

* Add more tests for `@pattern`

* Add entry to `CHANGELOG.next.toml`

* Fix a `@length` + `@pattern` test case

* Remove unused binding in `ConstrainedStringGeneratorTest`

* Remove calls to `trimIndent`

* Use raw Rust strings instead of `escapedPattern`

* Require `regex 1.5.5` instead of `1.7.0`

* Use `Writable`s in `TraitInfo`

* Use single `rust` call for `impl $name` block

* Move `supportedStringConstraintTraits` to `Constraints.kt`

* Fix error message mentioning wrong `ignoreUnsupportedConstraintTraits` key

* Fix usage of `:W` in `rustTemplate` and raw Rust strings

* Use shorthand form for `PatternTrait.validationErrorMessage`

* Fix protocol tests by adjusting the validation message

* Add uses of `@pattern` in `constraints.smithy` model

* Fix broken `RestJsonMalformedPatternReDOSString` test

* Move `TraitInfo` to its own module and separate string-specific details

* Update codegen-core/common-test-models/constraints.smithy

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

* Fix nits in `constraints.smithy`

* Add license to `TraitInfo.kt`

* Make `StringTraitInfo.fromTrait` not return a nullable

* Remove overzealous formatting

* Add some padding to json in `fixRestJsonMalformedPatternReDOSString`

* Add `compile_regex` function for `@pattern` strings

* Add helpful error message when regexes fail to compile

* Add missing coverage in `constraints.smithy`

* Fix examples in `constraints.smithy`

* Fix failing test

* Combine writables in `ConstrainedStringGenerator`

* Fix uses of `Writable.join`

* Use `expect` over `unwrap_or_else`

* Use `once_cell::sync::Lazy` over `once_cell::sync::OnceCell`

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