feat: support nested t and msg

[timofei-iatsenko]

Port of lingui/js-lingui#2625

[codecov]

Codecov Report

❌ Patch coverage is 95.23810% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 94.84%. Comparing base (1aebcb5) to head (c11aedc).

Files with missing lines	Patch %	Lines
crates/lingui_macro/src/macro_utils.rs	95.23%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #248   +/-   ##
=======================================
  Coverage   94.84%   94.84%           
=======================================
  Files           9        9           
  Lines        2327     2348   +21     
=======================================
+ Hits         2207     2227   +20     
- Misses        120      121    +1     

Flag	Coverage Δ
unittests	94.84% <95.23%> (+<0.01%)	⬆️

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Files with missing lines	Coverage Δ
crates/lingui_macro/src/macro_utils.rs	92.00% <95.23%> (+0.22%)	⬆️

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