Mass rename Ebb and relatives to Block (#1365)

* Manually rename BasicBlock to BlockPredecessor

BasicBlock is a pair of (Ebb, Inst) that is used to represent the
basic block subcomponent of an Ebb that is a predecessor to an Ebb.

Eventually we will be able to remove this struct, but for now it
makes sense to give it a non-conflicting name so that we can start
to transition Ebb to represent a basic block.

I have not updated any comments that refer to BasicBlock, as
eventually we will remove BlockPredecessor and replace with Block,
which is a basic block, so the comments will become correct.

* Manually rename SSABuilder block types to avoid conflict

SSABuilder has its own Block and BlockData types. These along with
associated identifier will cause conflicts in a later commit, so
they are renamed to be more verbose here.

* Automatically rename 'Ebb' to 'Block' in *.rs

* Automatically rename 'EBB' to 'block' in *.rs

* Automatically rename 'ebb' to 'block' in *.rs

* Automatically rename 'extended basic block' to 'basic block' in *.rs

* Automatically rename 'an basic block' to 'a basic block' in *.rs

* Manually update comment for `Block`

`Block`'s wikipedia article required an update.

* Automatically rename 'an `Block`' to 'a `Block`' in *.rs

* Automatically rename 'extended_basic_block' to 'basic_block' in *.rs

* Automatically rename 'ebb' to 'block' in *.clif

* Manually rename clif constant that contains 'ebb' as substring to avoid conflict

* Automatically rename filecheck uses of 'EBB' to 'BB'

'regex: EBB' -> 'regex: BB'
'$EBB' -> '$BB'

* Automatically rename 'EBB' 'Ebb' to 'block' in *.clif

* Automatically rename 'an block' to 'a block' in *.clif

* Fix broken testcase when function name length increases

Test function names are limited to 16 characters. This causes
the new longer name to be truncated and fail a filecheck test. An
outdated comment was also fixed.

cranelift/filetests/filetests/isa/x86/shrink-multiple-uses.clif

@@ -3,16 +3,16 @@ set opt_level=speed_and_size
 target x86_64
 
 function %test_multiple_uses(i32 [%rdi]) -> i32 {
-ebb0(v0: i32 [%rdi]):
+block0(v0: i32 [%rdi]):
 [DynRexOp1rcmp_ib#7083,%rflags]     v3 = ifcmp_imm v0, 0
 [Op2seti_abcd#490,%rax]             v1 = trueif eq v3
 [RexOp2urm_noflags#4b6,%rax]        v2 = bint.i32 v1
-[Op1brib#70]                        brif eq v3, ebb1
-[Op1jmpb#eb]                        jump ebb2
+[Op1brib#70]                        brif eq v3, block1
+[Op1jmpb#eb]                        jump block2
 
-ebb2:
+block2:
 [Op1ret#c3]                         return v2
 
-ebb1:
+block1:
 [Op2trap#40b]                       trap user0
 }