Remove frontend AST pattern matching (WIP)

[fonsp]

This will remove the lezer_template pattern matching system (#1849): it has become unmaintainable and the advantage is not toooo big. This will unblock #2980 . The new parser in #2980 is also much more "verbose", so implementing the same functionality with standard TreeCursor API becomes simpler.

Changes

The lezer_template` pattern matching was removed

The scope merging system was removed

pkg_bubble_plugin.js rewritten based on TreeCursor.

scopestate_statefield.js rewritten based on TreeCursor. The new version is less precise, but much smaller.

Try this Pull Request!

Open Julia and type:

julia> import Pkg
julia> Pkg.activate(temp=true)
julia> Pkg.add(url="https://github.com/fonsp/Pluto.jl", rev="remove-ast-pattern-matching")
julia> using Pluto