RFR: 8322971: KEM.getInstance() should check if a 3rd-party security provider is signed

[Valerie Peng]

On Wed, 3 Jan 2024 20:41:06 GMT, Weijun Wang <weijun at openjdk.org> wrote:

> `KEM.getInstance` now checks if the implementation is from a signed provider if it's not builtin to JDK.
> 
> Several adjustments to the test:
> 1. Put one impl in `SunEC` to pretend it's builtin. This is necessary to test for provider selection.
> 2. When there is no need to choose a provider, use reflection to create a `KEM` object that bypasses the `getInstance` call.

Looks good.

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Marked as reviewed by valeriep (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/17253#pullrequestreview-1812191658