fixes https://github.com/flutter/flutter/issues/123112

### Description
1. Add proper M3 indicator height aka`IndictorWeight` from the M3 specs for the primary tab bar with label indicator size.
https://github.com/flutter/flutter/blob/db6074ade4e4fde664e6258d671faf356e1b6e85/dev/tools/gen_defaults/data/navigation_tab_primary.json#L9
(this was held due to `indicatorWeight` having a hard-coded value) 

and added a secondary tab bar indicator height.
2. Set a minimum value for the rounded indicator to maintain the indicator shape.
3. With proper indicator height, the rounded indicator position is also fixed.
4. Fix round indicator is shown for the primary tab bar with tab indicator size.
5. Above changes fix https://github.com/flutter/flutter/issues/123112.
6. Fix the `startOffset` const value from https://github.com/flutter/flutter/pull/125036  to match docs and move it to a variable.