Bunch of bug fixes for ArrayBuffer & ListBuffer

[marcelocenerine]

• fix Patch throws an exception on out of bounds indices #398 (Buffer.patch throws out of bound index exception) by dropping validation in View.Patched
• fix patchInPlace throws a class cast exception #407 (ListBuffer.patchInPlace throws class cast exception) by clipping index/count to safe values
• fix various issues in ArrayBuffer.patchInPlace causing out of bound index exceptions
• fix ArrayBuffer#clear still references “removed” elements #385 (ArrayBuffer.clear not dereferencing cleared elements)
• Ensure that index passed into ArrayBuffer's apply and update is within bounds. This fix uncovered other issues in addOne and insert

Note: each fix is in a separate commit

[marcelocenerine]

renamed end to size0 as the former is misleading

[julienrf]

Aren’t bounds already checked by the underlying array access?

[marcelocenerine]

the underlying array can be larger than the ArrayBuffer in many situations:

import strawman.collection.mutable.ArrayBuffer
val a = ArrayBuffer(1)
a: strawman.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(1)

scala> a.remove(0)
res2: Int = 1

scala> a(0)
res3: Int = 0

scala> val b = ArrayBuffer.empty[Int]
b: strawman.collection.mutable.ArrayBuffer[Int] = ArrayBuffer()

scala> b(0)
res4: Int = 0

scala> val c = ArrayBuffer(1, 2, 3)
c: strawman.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(1, 2, 3)

scala> c.clear()

scala> c.size
res6: Int = 0

scala> c(0)
res7: Int = 1

[marcelocenerine]

in summary:

• when an empty ArrayBuffer is created, its underlying array will have size == 16
• when an ArrayBuffer's element is removed, the underlying array remains with the same size (only the buffer's size gets decremented)

[julienrf]

Thanks Marcelo :)