Disable Show all titles for Linechart

- Statistically most people make use of only two axes at a time when using the line chart. v0.40.0 by default enables all four axes Sidetitles which can be very confusing to a new user.
- A suggestion could be making use of a bool List in the FlTitleData class which will allow the user to list axes they want to show. much like what Flutter does in the EdgeInsets.fromLTRB() methods

**Example:**

`titlesData: FlTitlesData(
show: true,//Use bool List here
topTitles: SideTitles(showTitles: false),
rightTitles: SideTitles(showTitles: false),
bottomTitles: SideTitles(
showTitles: true,
rotateAngle: -40,
reservedSize: 26,`
.....

Start with the FlTitlesData and SideTitles API shown in the issue, then trace how line-chart title visibility defaults are applied. Compare the current default behavior with the requested per-axis selection and identify the relevant line-chart tests or examples; done means users can choose visible axes without manually disabling each side and existing title behavior remains covered.

Written by the indexing model from the issue text.