add attribute resize tracking

[aardgoose]

Untangle overloading of BufferAttribute.dynamic property, re #14730

.dynamic sets buffer usage expectations as documented.

.updateRange works as documented if dynamic = false. (currently updates entire buffer)

.setArray() and .copy() are safe to use if dynamic = true. (currently produces error)

By default gl.bufferSubData is used for updates except in resize operations.

(a flag to select update mechanism could be added if required )

[Mugen87]

I'm a bit irritated now. I always thought three.js does not allow to resize buffer attributes. If an app needs a bigger attribute buffer for some reasons, it has to create a new attribute. Or create a sufficient sized buffer in the forefront.

[aardgoose]

Some developers (not myself) were resizing them it seems, which is what started the initial discussion referred to in #14730.

After the changes I added which allowed you to drop the arrays from the JS side, after the GPU had been updated ( via the onUpload() callback) - this user 'requirement' came out the woodwork resulted in dynamic flag overloading.

[Mugen87]

Does the following error message still make sense?

https://github.com/mrdoob/three.js/pull/15798/files#diff-54f00f0a09b102e7d4bffbf907becd3aR89

[aardgoose]

Nothing bad appears to happen passing an empty TypedArray in the count = 0 error case.
Tested on Chrome/FF/IE11 on Windows 10, so maybe a pointless error other than pointing to programming error elsewhere.

Maybe errors on other platforms though?