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outdated comment was also fixed.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/regalloc/constraints.clif

@@ -6,7 +6,7 @@ target i686
 
 ; Tied operands, both are killed at instruction.
 function %tied_easy() -> i32 {
-ebb0:
+block0:
     v0 = iconst.i32 12
     v1 = iconst.i32 13
     ; not: copy
@@ -17,7 +17,7 @@ ebb0:
 
 ; Tied operand is live after instruction.
 function %tied_alive() -> i32 {
-ebb0:
+block0:
     v0 = iconst.i32 12
     v1 = iconst.i32 13
     ; check: $(v0c=$V) = copy v0
@@ -30,7 +30,7 @@ ebb0:
 
 ; Fixed register constraint.
 function %fixed_op() -> i32 {
-ebb0:
+block0:
     ; check: ,%rax]
     ; sameln: v0 = iconst.i32 12
     v0 = iconst.i32 12
@@ -43,7 +43,7 @@ ebb0:
 
 ; Fixed register constraint twice.
 function %fixed_op_twice() -> i32 {
-ebb0:
+block0:
     ; check: ,%rax]
     ; sameln: v0 = iconst.i32 12
     v0 = iconst.i32 12
@@ -60,7 +60,7 @@ ebb0:
 
 ; Tied use of a diverted register.
 function %fixed_op_twice() -> i32 {
-ebb0:
+block0:
     ; check: ,%rax]
     ; sameln: v0 = iconst.i32 12
     v0 = iconst.i32 12