Use name_val instead of JS.sourcetext

[aviatesk]

Use the name_val attribute directly to retrieve identifier names inside K"inert" nodes, instead of going through sourcetext. This avoids a crash when SyntaxTree nodes have LineNumberNode provenance (which occurs for nodes created via expr_to_est during old-style macro expansion), since sourcetext would fail with MethodError on such nodes.

Also simplify the foreach_inert_identifier /
foreach_identifier_in_inert helpers by removing the unnecessary _-prefixed indirection.

Fixes #583

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 67.74%. Comparing base (018aa0b) to head (4747008).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #584      +/-   ##
==========================================
+ Coverage   67.72%   67.74%   +0.01%     
==========================================
  Files          51       51              
  Lines        8311     8315       +4     
==========================================
+ Hits         5629     5633       +4     
  Misses       2682     2682              

Flag	Coverage Δ
JETLS.jl	67.74% <100.00%> (+0.01%)	⬆️

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