docs(material/slider): clarify behavior of slider range thumbs (#27846)

* docs(material/slider): clarify behavior of slider range thumbs

Clarifies possible behavior/values of matStartThumb and matEndThumb in
slider component 'Selecting a range' documentation.

Addresses #27837

* correct names of slider thumbs and streamline language

* small wording update for clarity

* add 'the' in front of reference to thumb

Author: stephanietuerk

src/material/slider/slider.md

@@ -16,9 +16,11 @@ respectively. The initial value is set to the minimum value unless otherwise spe
 ```
 
 ### Selecting a range
-A `<mat-slider>` can be converted into a range slider by projecting both a `matStartThumb` and a
-`matEndThumb` into it. Each of the thumbs has an independent value, but they won't be allowed to
-overlap and they're still bound by the same `min` and `max` from the slider.
+A `<mat-slider>` can be converted into a range slider by projecting both a `matSliderStartThumb` and a
+`matSliderEndThumb` into it. Each thumb has its own value, but both are still
+constrained by the slider's `min` and `max` values. The `matSliderStartThumb` cannot have a value
+greater than that of the `matSliderEndThumb` and the `matSliderEndThumb` cannot have a value less than
+that of the `matSliderStartThumb`, though they both may have the same value.
 
 ```html
 <mat-slider>