(aws_rds): signature of `AuroraMysqlEngineVersion.of` doesn't make sense

### Describe the bug

https://docs.aws.amazon.com/cdk/api/v2/docs/aws-cdk-lib.aws_rds.AuroraMysqlEngineVersion.html#static-ofauroramysqlfullversion-auroramysqlmajorversion

> `public static of(auroraMysqlFullVersion: string, auroraMysqlMajorVersion?: string): AuroraMysqlEngineVersion`

if `auroraMysqlFullVersion` (most specific) is required and `auroraMysqlMajorVersion` (less specific) is optional, why would you ever provide `auroraMysqlMajorVersion` arg?

More to the point, it seems there is no way of specifying a database engine such that it does not pin the full minor version?

All the provided constants like `VER_3_10_1` are fully specified too.

https://docs.aws.amazon.com/cdk/api/v2/docs/aws-cdk-lib.aws_rds.DatabaseCluster.html#autominorversionupgrade option is provided, but how does that fit if we're also fully specifying the minor version? Would subsequent deploys of the stack revert the db back to the specified minor version after auto upgrades had been applied?

### Regression Issue

- [ ] Select this option if this issue appears to be a regression.

### Last Known Working CDK Library Version

_No response_

### Expected Behavior

Should be able to specify only the major version and have the latest minor version automatically deployed

### Current Behavior

Unclear

### Reproduction Steps

Create an RDS db using the provided interface

### Possible Solution

_No response_

### Additional Information/Context

_No response_

### AWS CDK Library version (aws-cdk-lib)

2.221.1

### AWS CDK CLI version

2.1031.1 (build a560d1e)

### Node.js Version

v22.21.0

### OS

macOS 14.6

### Language

Python

### Language Version

3.11

### Other information

_No response_

Start with the AuroraMysqlEngineVersion.of API documentation and the DatabaseCluster autoMinorVersionUpgrade option described in the issue. Compare the current API contract with AWS RDS engine-version behavior and determine whether major-only selection is supported; done means the intended version-pinning and upgrade behavior is clarified, with any required API, documentation, and test changes identified.

Written by the indexing model from the issue text.