[Android JCA] Support RSA PKCS#8 imports when providers hide CRT parameters

## Problem

On the tested Android API 24-26 providers, `KeyFactory` accepts a valid RSA PKCS#8 encoding but returns a private-key object that does not implement `RSAPrivateCrtKey`. The JNI backend then rejects the key because its import-time validation and private JWK export require the CRT components.

The tested API 36 provider returns an `RSAPrivateCrtKey` for the same generate, encode, and re-import path.

## Provider Evidence

On the Android API 24 x86_64 image with AndroidOpenSSL 1.0:

- RSA generation returns `OpenSSLRSAPrivateCrtKey`.
- Re-importing the generated key's PKCS#8 encoding returns `OpenSSLRSAPrivateKey`.
- The imported key does not implement `RSAPrivateCrtKey`.
- `KeyFactory.getKeySpec(..., RSAPrivateCrtKeySpec.class)` returns a plain `RSAPrivateKeySpec`, so the provider still does not expose the CRT values.

API 25 and 26 reproduce the same `package:webcrypto` PKCS#8 import failure. API 36 re-imports the generated encoding as `OpenSSLRSAPrivateCrtKey` and passes the shared RSA-PSS suite with the parameter-order fix.

The shared RSA key layer affects RSASSA-PKCS1-v1_5, RSA-OAEP, and RSA-PSS.

## Constraint

The backend checks CRT consistency during import so malformed private keys fail as `FormatException` before use. Private JWK export requires `n`, `e`, `d`, `p`, `q`, `dp`, `dq`, and `qi`. Removing the CRT requirement would weaken import validation and leave private JWK export incomplete.

## Decision Needed

Choose one source for provider-independent RSA components:

- Add a small reviewed PKCS#8/DER parser to the JNI backend and retain the parsed components beside the persistent JCA key.
- Use a reviewed ASN.1 dependency for the same parse-and-retain design.
- Restrict the supported Android provider/API matrix and document the limitation.

The API 24 experiment rules out direct CRT extraction through `KeyFactory.getKeySpec`.

## Acceptance Criteria

- Valid generated and supplied PKCS#8 keys import on the selected Android provider/API matrix.
- Malformed RSA keys fail during import with `FormatException`.
- PKCS#8 and private JWK exports preserve the imported key material.
- Persistent JCA key ownership and isolate-unsendable behavior remain intact.
- Focused RSASSA, RSA-OAEP, and RSA-PSS tests pass.
- The shared RSA suites run on every Android API/provider combination selected for backend support.

## Reproduced Results

- API 24 x86_64 RSA-PSS selection: 22 passed and 344 failed after the private-key import prerequisite failed.
- API 25 and 26 x86_64 focused RSA-PSS tests fail at the same private-key import step.
- API 36 x86_64 RSA-PSS selection with the parameter-order fix: 366 passed.

Related: #323, #340, #341

Start with the JNI backend's RSA import validation and private JWK export path, using the API 24–26 provider evidence as the baseline. Review the three proposed sources for provider-independent components and related issues #323, #340, and #341 before choosing an approach. Done means the selected provider/API matrix passes the focused RSASSA, RSA-OAEP, and RSA-PSS suites while preserving malformed-key rejection, exports, JCA ownership, and isolate-unsendable behavior.

Written by the indexing model from the issue text.