[CodeExtractor] Replace uses of extracted bitcasts in out-of-region lifetime markers

CodeExtractor handles bitcasts in the extracted region that have
lifetime markers users in the outer region as outputs. That
creates unnecessary alloca/reload instructions and extra lifetime
markers. The patch identifies those cases, and replaces uses in
out-of-region lifetime markers with new bitcasts in the outer region.

**Example**
```
define void @foo() {
entry:
  %0 = alloca i32
  br label %extract

extract:
  %1 = bitcast i32* %0 to i8*
  call void @llvm.lifetime.start.p0i8(i64 4, i8* %1)
  call void @use(i32* %0)
  br label %exit

exit:
  call void @use(i32* %0)
  call void @llvm.lifetime.end.p0i8(i64 4, i8* %1)
  ret void
}
```

**Current extraction**
```
define void @foo() {
entry:
  %.loc = alloca i8*, align 8
  %0 = alloca i32, align 4
  br label %codeRepl

codeRepl:                                         ; preds = %entry
  %lt.cast = bitcast i8** %.loc to i8*
  call void @llvm.lifetime.start.p0i8(i64 -1, i8* %lt.cast)
  %lt.cast1 = bitcast i32* %0 to i8*
  call void @llvm.lifetime.start.p0i8(i64 -1, i8* %lt.cast1)
  call void @foo.extract(i32* %0, i8** %.loc)
  %.reload = load i8*, i8** %.loc, align 8
  call void @llvm.lifetime.end.p0i8(i64 -1, i8* %lt.cast)
  br label %exit

exit:                                             ; preds = %codeRepl
  call void @use(i32* %0)
  call void @llvm.lifetime.end.p0i8(i64 4, i8* %.reload)
  ret void
}

define internal void @foo.extract(i32* %0, i8** %.out) {
newFuncRoot:
  br label %extract

exit.exitStub:                                    ; preds = %extract
  ret void

extract:                                          ; preds = %newFuncRoot
  %1 = bitcast i32* %0 to i8*
  store i8* %1, i8** %.out, align 8
  call void @use(i32* %0)
  br label %exit.exitStub
}
```

**Extraction with patch**
```
define void @foo() {
entry:
  %0 = alloca i32, align 4
  br label %codeRepl

codeRepl:                                         ; preds = %entry
  %lt.cast1 = bitcast i32* %0 to i8*
  call void @llvm.lifetime.start.p0i8(i64 -1, i8* %lt.cast1)
  call void @foo.extract(i32* %0)
  br label %exit

exit:                                             ; preds = %codeRepl
  call void @use(i32* %0)
  %lt.cast = bitcast i32* %0 to i8*
  call void @llvm.lifetime.end.p0i8(i64 4, i8* %lt.cast)
  ret void
}

define internal void @foo.extract(i32* %0) {
newFuncRoot:
  br label %extract

exit.exitStub:                                    ; preds = %extract
  ret void

extract:                                          ; preds = %newFuncRoot
  %1 = bitcast i32* %0 to i8*
  call void @use(i32* %0)
  br label %exit.exitStub
}
```

Reviewed By: vsk

Differential Revision: https://reviews.llvm.org/D90689