ImplicitReceiverValue is mutable and FIR body resolve could alter it
while analysing code with smartcast. Hence, previously the IDE may see
inconsistent receiver values for a local scope. For example
```
open class A
interface Foo {
fun foo()
}
fun A.bar() {
if (this is Foo) {
// scope here has implicit receiver type to be `A` rather than `it<A, Foo>`
}
}
```
This change creates snapshots for local statements so later changes
during body resolve won't affect the collected context.
Tianyu Geng
e5b9d667c0