[Bug] Stack does not work correctly if xAxis is value type

### Version

5.4.2

### Link to Minimal Reproduction

https://echarts.apache.org/examples/en/editor.html?c=line-simple&code=PYBwLglsB2AEC8sDeAoWsAeBBDEDOAXMmurGAJ4gCmRA5AG4CGANgK5W0A0JAvt-uRz4iqUmUo1YDFu1q9-sPFQBOEKoVgBtEulFjYAE0ZhGRTZoCMABk4WArFYC6nLQCYbrgMxOXm751dXABZnLSCPCwAOUM0HW087GIA2GwsggHYY9I8Ux2cdUgpqOmYIaA4FMTwTAGMAawJaMHUwOTE-Ar0xIxMzSw8AThj3TnCY_yDE33DbK1hnWJts5JsMrJy8ysKJErKKgvRqxnrG5uq20g6xEkcUHgBuIA

### Steps to Reproduce

1. create simple line chart with both xAxis and yAxis as value type
2. add stack property
3. check the result

### Current Behavior

Echart is selecting xAxis as stackable

### Expected Behavior

yAxis should get selected as stackable or there should be option to provide which axis should be consider as stackable.

### Environment

```markdown
- OS:
- Browser:
- Framework:
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### Any additional comments?

_No response_

Start with the linked minimal reproduction and verify the stacked line chart when both xAxis and yAxis use value types. Trace how the stack property chooses an axis, then define and test behavior where yAxis is selected or the stack axis can be specified; done means the reproduction stacks on the intended axis.

Written by the indexing model from the issue text.