feat[tool]: add node_id map to source map

[charles-cooper]

add node_id map to source map which links directly back to the AST output to improve source code integrations for third parties

refactor:

• get rid of vyper.codegen.core.getpos()
• rename IRnode.source_pos to IRnode.ast_source
• thread ast_source through to sourcemap generation
• refactor a couple places in codegen which were passing IRnode to Expr constructor

i also rewrote the source map compression routine a bit. it might have gotten broken but at this point i don't think anybody really uses the compressed source map (i checked with ape and hardhat here and waiting to hear back from slither), they prefer the other formats.
other major tooling:

• brownie uses the compressed source map but it has been sunset, nothing we can do there
• titanoboa uses the vyper ast directly, in a way very similar to the export here actually
• not sure what foundry does, they don't support vyper now, they might in the future but idk if it would really be a blocker if we dropped the compressed source map

fixes #1609

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Commit message

this commit adds a new, AST-based map to the source map which links
program counters (pcs) directly back to the AST output. this should
improve the ability of third parties to implement source code
integrations (debuggers, storage map tracers, etc).

refactors:
- get rid of `vyper.codegen.core.getpos()`
- rename `IRnode.source_pos` to `IRnode.ast_source`
- refactor a couple places in codegen which were passing `IRnode`s to
  the `Expr` constructor
- rewrote the source map compression routine a bit. it might have gotten
  broken but at this point the compressed source map does not seem
  widely used.

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[codecov-commenter]

Codecov Report

Attention: Patch coverage is 98.16514% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 86.20%. Comparing base (9428196) to head (b952144).

Files	Patch %	Lines
vyper/codegen/expr.py	94.73%	1 Missing ⚠️
vyper/ir/compile_ir.py	95.23%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3811      +/-   ##
==========================================
- Coverage   86.21%   86.20%   -0.02%     
==========================================
  Files          92       92              
  Lines       13998    14008      +10     
  Branches     3076     3077       +1     
==========================================
+ Hits        12068    12075       +7     
- Misses       1494     1496       +2     
- Partials      436      437       +1     

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