Remove the need for operation type aliasing in codegen (#1710)

* remove: need for operation type aliasing
rename: FluentClientGenerics.sendBounds params to be more accurate
update: FlexibleClientGenerics.sendBounds impl for readability
update: type of FluentClientGenerator input param `retryPolicyType` to be `Any` with a default of `RustType.Unit`
update: PaginatorGenerator to take retryPolicy as an input
chore: fix some spelling and grammar issues
remove: redundant `nextTokenEmpty` function from PaginatorGenerator

* Update CHANGELOG.next.toml

Co-authored-by: John DiSanti <jdisanti@amazon.com>

* add: `writable` property to RustType that returns the type as a Writable
add: test for RustType writable
add: `writable` property to RuntimeType that returns the type as a Writable
update: FluentClientGenerator to take a writable for retry

* format: run formatter

Co-authored-by: John DiSanti <jdisanti@amazon.com>