Enable setting and getting multiple bits in `Bitmaps.sol`

🧐 Motivation

• The Bitmaps library can be greatly expanded in its usefulness if setting and getting multiple bits is enabled

This would be helpful, e.g., in an NFT bitmap-based airdrop where we start with 1-bits and switch them to 0 as mints occur.
This would also be helpful in the case where a protocol is using bitpacking (e.g., this is directly useful in Panoptic), as in: https://twitter.com/cryptojesperk/status/1613207330782416897?s=20&t=dDcU6hQPJEGzoo8sX8PJ8A

📝 Details
These new functions are added via function overloading (the argument list is changed from taking an index to a startIndex and num):

• set(BitMap storage bitmap, uint256 startIndex, uint256 num)
• get(BitMap storage bitmap, uint256 startIndex, uint256 num)
• setTo(BitMap storage bitmap, uint256 startIndex, uint256 num, bool value)
• unset(BitMap storage bitmap, uint256 startIndex, uint256 num)

Where "startIndex" is the starting index of the first bit to interact with. "num" is the number of bits to interact with (set or unset) from the startIndex onwards.

Consider the following 256 bits (32 bytes, or 1 word) example:

exampleBitmap = 0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

Currently, we can set or unset 1 bit at a time. With these new functions, we can set n bits at once.

For example:

exampleBitmap = exampleBitmap.set(5, 10);

sets the bits starting at index 5 to 15 to 1 - and leaves the rest at 0 - in a single function call:

0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000011111111110000

And we can get those bits back:

exampleBitmap = exampleBitmap.get(5, 10);

Returns the bits:

1111111111

The bits can be returned in various formats to be decided. Potentially as an array of uint256s. An event would be emitted also detailing the start index and the number of bits that are returned.

The difficult parts will be when bits are set across overlapping _data elements, but can be handled, among other complex situations (which can all be handled).

Start by reviewing Bitmaps.sol and its existing single-bit operations. Clarify the return representation and boundary behavior for ranges crossing _data elements, then define tests covering setting, getting, and unsetting ranges; the work is done when the overloaded APIs and their edge cases are specified and covered.