Move generic term rewriting features to Metatheory.jl

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This is an attempt to unify the Symbolics ecosystem following a layered protocol approach, in order to maintain code as general as possible without sacrificing all the performance optimizations of SU, and in order to extend SU support to e-graph rewriting, non-evaluating symbolic-replacement rules (--> operator) and a new, drop-in, alternative friendly syntax:

• TermInterface is the glue package between all symbolics manipulation packages
• Metatheory.jl provides all the generic term rewriting utilities (Rule, ACRule, EGraphs, matchers, Rewriters,...) on any type that satisfies TermInterface.jl
• SymbolicUtils.jl provides the specifically optimized types and simplification rules for mathematical symbolic expressions (Add, Mul, Div, PolyForm), and code generation etc...

This follows the the last diagram of https://discourse.julialang.org/t/a-recap-of-the-state-of-the-symbolics-ecosystem/68022 and should in principle simplify the dependencies, CI fragmentation and versioning, in contrast to #352 that would have provided a lot of CI fragmentation and dependency versioning hell

This needs JuliaSymbolics/Metatheory.jl#77 to be merged and released first

The imported modules from Metatheory are

using Metatheory # generic term rewriting 
using Metatheory.Rules # RewriteRule, ACRule, DynamicRule
using Metatheory.Rewriters # Rewriter combinators
using Metatheory.SUSyntax # Use the SymbolicUtils rule language for defining rules.

If you want to try out the new syntax, replace SUSyntax with NewSyntax. In the new syntax, symbols in patterns (x) are slot variables, x... is used for segment variables, => for substitution rules, |> for dynamic rules, == and != for bidirectional e-graph specific rules.

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All the stuff works if you locally clone and add the SU#lower_to_mt and MT#lower_from_su branches

Some stuff left to do:
Merge and release JuliaSymbolics/Metatheory.jl#77
Merge master into this branch
Fix timerewrite
Fix the benchmark tests and compare them, in case, tweak performance of lowered features

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@shashi could you please retrigger buildkite benchmark?

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Everything should be working and this PR should be ready to be reviewed

[shashi]

It seems the buildkite failure is unrelated?

[shashi]

Okay now we get a nice error message that is relevant.

[0x0f0f0f]

Okay now we get a nice error message that is relevant.

Fact is that we want to use @rule from Metatheory when benchmarking this branch and @rule from SU when benchmarking master. How to proceed?

[0x0f0f0f]

Okay now we get a nice error message that is relevant.

Fact is that we want to use @rule from Metatheory when benchmarking this branch and @rule from SU when benchmarking master. How to proceed?

Dumb question. SymbolicUtils.jl re-exports Metatheory.jl's @rule in this PR. Should work now.

[codecov-commenter]

Codecov Report

Merging #368 (987f6f6) into master (5860207) will increase coverage by 1.49%.
The diff coverage is 87.50%.

@@            Coverage Diff             @@
##           master     #368      +/-   ##
==========================================
+ Coverage   83.54%   85.03%   +1.49%     
==========================================
  Files          12       10       -2     
  Lines        1489     1203     -286     
==========================================
- Hits         1244     1023     -221     
+ Misses        245      180      -65     

Impacted Files	Coverage Δ
src/code.jl	81.67% <ø> (ø)
src/utils.jl	57.74% <ø> (-0.91%)	⬇️
src/types.jl	84.99% <60.00%> (ø)
src/rule.jl	96.15% <100.00%> (+11.07%)	⬆️

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[shashi]

🎉