xAxis is showing scaled values automatically and ignoring our custom values

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## What did you do?

I gave dataset as (6,10), (7,30), (26,22), (26,0)

## What did you expect to happen?

I expected to show line chart of these values

## What happened instead?

it automatically showed x lables such as 8,12,16,20 which ruined the graph.

## Charts Environment

**Charts version/Branch/Commit Number:**
**Xcode version:**
**Swift version:**
**Platform(s) running Charts:**
**macOS version running Xcode:**

## Demo Project

ℹ Please link to or upload a project we can download that reproduces the issue.

No source file, test, or demo project is named. Start by reproducing the chart with the points (6,10), (7,30), (26,22), and (26,0), then trace the x-axis label generation; done means the chart preserves the intended custom x values without unwanted scaled labels.

Written by the indexing model from the issue text.