Less local variable renaming in compiled code

[RealyUniqueName]

See #9035
Closes #9296

Finally I've managed to implement something bearable.

This takes into account target rules for local variables scoping.
For example this sample:

var tmp = 0;
var x = 1;
tmp = x;
var x = 2;
tmp = x;
var x = 3;
tmp = x;

when compiled for js:

var tmp = 0;
var x = 1;
tmp = x;
var x = 2;
tmp = x;
var x = 3;
tmp = x;

to cs (no shadowing allowed):

int tmp = 0;
int x = 1;
tmp = x;
int x1 = 2;
tmp = x1;
int x2 = 3;
tmp = x2;

In conjunction with #9280 this will reduce amount of local variables generated for JS even more.

[nadako]

In conjunction with #9280 this will reduce amount of local variables generated for JS even more.

Wouldn't that re-introduce numbering though? Because you can't do let x in the same block multiple times.

[RealyUniqueName]

Wouldn't that re-introduce numbering though? Because you can't do let x in the same block multiple times.

Indeed.
Well, at least you won't see variables from sibling blocks in debugger )

[RealyUniqueName]

numbering

Actually, that depends on a user code.
E.g. this

var x = 123;
if(condition) {
  var x = 'hello';
  trace(x);
}
trace(x);

with #9280 will be compiled to

let x = 123;
if(condition) {
  let x = "hello";
  console.log(x);
}
console.log(x);

while without #9280 it will be

var x = 123;
if(condition) {
  var x1 = "hello";
  console.log(x1);
}
console.log(x);

[nadako]

Yes, and that's probably a more real-world case, so go for it :) It's just that the original example with same-block shadowing will not really be improved by let :)