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outdated comment was also fixed.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/verifier/simd-lane-index.clif

@@ -3,7 +3,7 @@ set enable_simd
 target x86_64
 
 function %insertlane_i32x4() {
-ebb0:
+block0:
     v0 = vconst.i32x4 [0 0 0 0]
     v1 = iconst.i32 42
     v2 = insertlane v0, 4, v1 ; error: The lane 4 does not index into the type i32x4
@@ -11,7 +11,7 @@ ebb0:
 }
 
 function %insertlane_b16x8() {
-ebb0:
+block0:
     v0 = vconst.b16x8 [false false false false false false false false]
     v1 = bconst.b16 true
     v2 = insertlane v0, 8, v1 ; error: The lane 8 does not index into the type b16x8
@@ -19,7 +19,7 @@ ebb0:
 }
 
 function %insertlane_f64x2() {
-ebb0:
+block0:
     v0 = vconst.f64x2 0x00
     v1 = f64const 0x0.1
     v2 = insertlane v0, 2, v1 ; error: The lane 2 does not index into the type f64x2
@@ -27,14 +27,14 @@ ebb0:
 }
 
 function %extractlane_i32x4() {
-ebb0:
+block0:
     v0 = vconst.i32x4 [0 0 0 0]
     v1 = extractlane v0, 4 ; error: The lane 4 does not index into the type i32x4
     return
 }
 
 function %extractlane_b8x16() {
-ebb0:
+block0:
     v0 = vconst.b8x16 0x00
     v1 = extractlane v0, 16 ; error: The lane 16 does not index into the type b8x16
     return