Each call to new_scope() should be matched with leave_scope()

[seanyoung]

The try catch blocks had an additional new_scope() which is incorrect. I think the extra scope is harmless but let's clean it up.

Rename new_scope() to enter_scope() as this matches leave_scope() better.

[codecov]

Codecov Report

Merging #1562 (4d13c4b) into main (a9e20d3) will increase coverage by 0.00%.
Report is 1 commits behind head on main.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1562   +/-   ##
=======================================
  Coverage   87.35%   87.36%           
=======================================
  Files         133      133           
  Lines       64126    64125    -1     
=======================================
+ Hits        56019    56021    +2     
+ Misses       8107     8104    -3     

Files	Coverage Δ
src/codegen/statements/mod.rs	96.77% <100.00%> (ø)
src/codegen/yul/statements.rs	98.13% <100.00%> (ø)
src/sema/statements.rs	93.80% <100.00%> (-0.01%)	⬇️
src/sema/symtable.rs	92.70% <100.00%> (ø)
src/sema/yul/block.rs	100.00% <100.00%> (ø)
src/sema/yul/for_loop.rs	95.14% <100.00%> (ø)
src/sema/yul/functions.rs	84.40% <100.00%> (ø)
src/sema/yul/mod.rs	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes