Adjust `SILFunctionBuilder` to allow distinct non-custom effects and to
interpret such "conflicting" guarantees to provide the strongest
guarantee. For example, annotating a function both `@_effects(readnone)`
and `@_effects(releasenone)` is equivalent to only annotating it
`@_effects(readnone)`.
First step to reapplying https://github.com/apple/swift/pull/68285 .
rdar://118216287
Functions which which consume their arguments will release them on any
branches where the arguments are unused. Users of `@_effects(readnone)`
and `@_effects(readonly)` may not consider this when annotating their
functions. Require that functions annotated thus are also annotated
@_effects(releasenone).
In order to support this, adjust SILFunctionBuilder to allow distinct
non-custom effects and to interpret such "conflicting" guarantees to
provide the strongest guarantee. For example, annotating a function
both `@_effects(readnone)` and `@_effects(releasenone)` is equivalent to
only annotating it `@_effects(readnone)`.
