Fix a whole bunch of binary literals which were the wrong size.  All were being silently zero extended to the correct width.

The commit after this changes { } and 0bxx literals to be of type bits<n> and not int.  This means we need to write exactly the right number of bits, and not rely on the values being silently zero extended for us.
TableGen: Change { } to only accept bits<n> entries when n == 1.

Prior to this change, it was legal to do something like

  bits<2> opc = { 0, 1 };
  bits<2> opc2 = { 1, 0 };
  bits<2> a = { opc, opc2 };

This involved silently dropping bits from opc and opc2 which is very hard to debug.

Now the above test would be an error.  Having tested with an assert, none of LLVM/clang was relying on this behaviour.

Thanks to Adam Nemet for the above test.
Change TableGen so that binary literals such as 0b001 are now sized.

Instead of these becoming an integer literal internally, they now become bits<n> values.

Prior to this change, 0b001 was 1 bit long.  This is confusing as clearly the user gave 3 bits.
This new type holds both the literal value and the size, and so can ensure sizes match on initializers.

For example, this used to be legal

bits<1> x = 0b00;

but now it must be written as

bits<2> x = 0b00;
Change BitsInit to inherit from TypedInit.

This is useful in a later patch where binary literals such as 0b000 will become BitsInit values instead of IntInit values.
Change the { } expression in tablegen to accept sized binary literals which are not just 0 and 1.

It also allows nested { } expressions, as now that they are sized, we can merge pull bits from the nested value.

In the current behaviour, everything in { } must have been convertible to a single bit.
However, now that binary literals are sized, its useful to be able to initialize a range of bits.

So, for example, its now possible to do

bits<8> x = { 0, 1, { 0b1001 }, 0, 0b0 }
Update BitRecTy::convertValue to allow if expressions with bit values on both sides of the if
Update Tablegen documents given that binary literals are now sized