[Bug] Line color doesn't follow the colors in visualmap

### Version

5.6.0

### Link to Minimal Reproduction

[demo](https://echarts.apache.org/examples/en/editor.html?code=PYBwLglsB2AEC8sDeAoWsDGwA2wBOAXLANprqwDkAxACwDMA7AJwDCAohQDRnrVNMAhABwAxAIxcelKiICCAEQGNJ5aSJZCAbAAYATCvLURchjSEHeVBroEBWNgIvSGQlvLbyn1WSyay2-tyqRj50miJeMvIMIjEUZAC6QbAAzgCmeBBpKUSkqqiq6GAAniBpRBTYENBpTuhp0FgAJuXIUqoAHrnaSe3kxblivYWwAL7JqinFALYARjgVGBB4GNi1E-RTczgAyhAAXq1i2hvoWNA1GGAAcgCu2Ng5sGB4t2mnsFU1OyVrRAUjZ6lVoUFI4CBNOrkADuELAAAsiHQ-qMpKj0MNYAA3CApW4AQ2wAFl8SBclIAaoSmUKiAshg0rD0lCmhBpg0UlBoERdB8UiAqjdbnMMkRbJxYH1ptUiGIPtN8V1YEwPtUAEr46AAc1alMKXzSP2KfzagPIWFwhBIFDwaUhEooWttDQomJG4z6Zxw-FyNrtXEoTrSLoSKI-wFuYAA8gAzDXa3WezDeq18fjxd18-HAaFEF5vDYejHJJr4sD4gBawGA01ymNL5fSYHJ-T6YNuKzSAAk0viWlaY4T0h9WezoJyYE88oC9SNoPj2RVAKemgHxzWAACkALnoASihVOBFUg7L35H2MDSABUD5Q8DmM4CizOk-h54vKIAAVMAuRkAfTA2TAqwnugMb4AqzbII-ZrUiCMa4GWQGwGeNRXjSlDsi8EAYPemZJrOhSviCX6_v-gEfKoIF4GB_yQYC0EVLBwDwWRp7nihIIWvgAjFNhhTooUbqbBGnYtoCxAULoejaAGQh0NoYg0Aw2gAHTirAQgCaoYkSboEgSlomi2DJTAqXpGnkFpeiBMqilCLoujGapTBmegFm6HQ0maAZRkmWpznWtpNABvJ2iaAwtgqrAQx9AJfGYh0sgdLi_xSHRlAYGWaRavg3EbCAwCcpAMAVPMYBgDWTgpNmubPK8aRkI-xQJUlprkKlFBYoSbwVVVea1fVyROhCyVUqARCaBsawxuBvJSJkWrwtNGwlWVtawHQM2qOc5bVAAMvisxpNgvVvPVKCjAA3EAA&_source=echarts-doc-preview&version=5.6.0&renderer=svg)

### Steps to Reproduce

See the demo

### Current Behavior

Add a visualmap to map an extra color dimension to color of line series.
The color of symbols are changed as expected, but the line color are not changed.

### Expected Behavior

Line color should follow the color of symbols and be a gradient if the colors of two points are different.

### Environment

```markdown
- OS:
- Browser:
- Framework:
```

### Any additional comments?

It works fine if the visualmap `dimension` is one of the axis dimensions.(like https://echarts.apache.org/examples/zh/editor.html?c=line-gradient)
[Adding another dimension and updating the option](https://echarts.apache.org/examples/zh/editor.html?c=line-gradient&code=PTAEAcCcFMBdYJbUgWgQcwHYHsYCgBjbTAZ1lABMBDWK0AXlAG0mAiAJgAZuVOA2XgFZWAGlABGcXwC6Ytlx79efURPYBOWcw7dOy3gHZV4gMyCt83fs4AOVTZlydigZ3WqDJi871Lxne3MnBV8BSQ8vYKs_dlU-G28Q_VNVdXZE6LCAFmMTTgyXFHFhMXYsoO0kvxUxU00owvEjWuKC0KK7FvE25PcxPPrKzJQuVS5HIcL2cVyDHqV2WNr2BIb29hNA-YEy1KztkZLQA261_XYaiX4D9mbQG32zhc7QdUjJ9b77istCvIj5gZeDMxDZ3r9fEDOEs1D8fIZeJtapw5k8oTlQek0UJVFlHh8EfwPFiCSjDMZrtjbBTUaSoV8-BMIQj_KlTnSiiDXiTmWTxDDJOD4XykVdabygeIMRITOyJUUjpI5cLJZc-Pj5U04oNNS8bKsOeIvgZxSqRgFQUKqkDpsZJICRjDBKbrSNRYI4a7dmI-PlpAA6AC2VHAAApQ1RIJAxAgAJQMAB8zH9Kcj0dACGksYA3IRiGRKDRoAAZBAFxjUWhBkOhgBmAFdMAREMRQKGELBoIH4wBvPCgUAwWD1yCYDOdwNMfK5gC-ObzpHIADcqAAbeslsvkCs0KjVsMNpstsftie9_uDuAjscdrtMbqz-fYcDHhigPsDkCgACyVAA1tAoDoJAVAUEgmDkKuCCYIBAAWyDQBeS5lvWa6_uAABczAXgOH4DvhJCwdgADuWG1muJDQCIOH4bAACe4DQFhADkRAQdB9bYPWJDMdR-EEcgSAkAAkpgFDQAAHlhnB8fxlAIIG0CkAgxBYewYhfjg5BUBJZbyYpynEDRA6BtB0myfxwZSYWnalmQ_qrkp6CwLBoAoBINEzhZ77GaAhEkWRFFUb59GMSxbGIJgnHcbxvmUZAQmieJ1niN5A5gQZJAqZg5m-aZOWgDJeU6VhlabvZjmYM5rnueInkXrIF6ILAjlYUwNF4fxjm1rA4VKZ2kCxXJoCdhJvWgMxADiIFgf1oBrsQ6AjfBoB0fNuk8Z53mdbRz4sR6ACkQ1yd142sf1yDHfxo1ndNoHgdpq6LctgESetZbMfVA6NQOsDYNgq6IJhPnXQl6DoMgLE6R9F5eReEkAIIbW1HW-ZWVClUWdmwFtqPDejmO2VuaVAQlFBJZJWF1fxM4NbJdFI2WKP8T2cMs75wEIOTYmUx5NN0xenMUMz-E7QOABG2DwNggYsb6R24-zw1_cDzHy59_PfbJ8VCSLuEhQxTETVBMFXQRRHEQAynRgaS6ugWrpRJME6AK7ruVOM09tBthcb0HQGbA7-VbNt2w7Tto7uWFuxu2Mk4jG0UylJMM4nPMpV9oDSHgM7ZkAA) can reproduce this issue too

Start with the linked minimal reproduction on ECharts 5.6.0 and trace the visualmap behavior for a line series using an extra color dimension. Compare symbol coloring with line rendering; done means line colors follow the symbol colors and form a gradient when adjacent points differ.

Written by the indexing model from the issue text.