* adding the lerp to Math class #9728

Adding the precise  interpolation from point x to y using factor t.

* Adding the documentation for Lerp function

Adding the lerp in doc support

* Documentation: Add more live examples

* Documentation: Correct format

* object callbacks

per previous request

added after call
added arguments to both calls

* faster function evaluation, missing comma

getElapsedTime() in TREE.Clock returns whole running time and not elapsed time from previous start. (#9692)

* getElapsedTime() returns whole running time

getElapsedTime() function returns incorrect value after stop() and start(), It returns whole working time from first run.
I changes adde this.elapsedTime = 0 in stop() function, so after next start() we can get correct elapsed time from last start()

Perhaps it's incorrect and suggested changes need new function, so Clock.js will have two functions:
- first one will return whole running time (as it is now)
- second will return elapsed time from last start

* Update Clock.js

* PolyhedronBufferGeometry: Initial commit

* PolyhedronBufferGeometry: Update docs

Reading clientHeight of canvas during every rAF causes layout thrashing and results in frame drops. Instead re-use the _height local variable available in current scope.

Corrected the spelling of argument in docs/manual/introduction/Creating-a-scene.html

- Move computation from fragment shader to vertex shader wherever possible
- Eliminate some dead shader code and comments
- Fix spelling of "Rayleigh"