[pkg/ottl] Add grammar utility to extract paths from statements

[edmocosta]

Description:

This PR is part of #29017, and adds a grammar utility to allow extracting ottl.path from parsed statements and expressions. The new functions will power the context inferrer utility (see draft), which implementation will basically gather all declared statement's Path.Context, and choose the highest priority one.

For the statements rewriter utility purpose, it changes the grammar.go file including a new field Pos lexer.Position into the ottl.path struct. This value is automatically set by the participle lexer and holds the path's offsets, being useful for identifying their positions in the raw statement, without using regexes an being coupled to the grammar's definition.

Additional changes:

This proposal uses the visitor pattern to gather all path's from the parsed statements. Considering the grammar's custom error mechanism (checkForCustomError) also works with a similar pattern, I've added the visitor implementation as part of the grammar objects, and refactored all checkForCustomError functions to be part of a validator visitor. Differently of the current implementation, it joins and displays all errors at once instead of one by one, IMO, it's specially useful for statements with more than one error, for example: set(name, int(2), float(1)).

* We can change it back do be error-by-error if necessary.
* If modifying the custom validator is not desired, I can roll those changes back keeping only the necessary code to extract the path's + Pos field.

Link to tracking Issue: #29017

Testing: Unit tests were added

Documentation: No changes

[TylerHelmuth]

@edmocosta I'm holding off on reviewing this until it is marked Ready, but I am interested.

[edmocosta]

@edmocosta I'm holding off on reviewing this until it is marked Ready, but I am interested.

I was running a few more tests and forgot to mark it as ready. Thanks @TylerHelmuth!