YQL-20380: Introduce LSP correct name resolution

Previous name resolution in a completion engine was poor, because it
just mapped a name for an expression and so redefinition was not working.
For example, a table name inference did not work on the following query:
```yql
$x = '/a' $x = $x || 'b'; $x = $x || 'c'; FROM plato.$x SELECT #;
```
But now it works. And also there was an issue with names visibility,
because names were resolved like for `letrec`, not `let`. It was fixed.

The new name resolution analyses the whole query and uses not only a name
for an identifier lookup, but also its position in text. Each named node
entry now classified as definition and a reference. There is a way to map
each reference to a definition. In future it will be a basis for named nodes
"go to definition", "find references", "rename" LSP methods.
commit_hash:ceeecbe2a59aa4d82ceb59ef930af5659dcd5ff7

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