[Lang] Adds source code statement

[dmed256]

Description

• Adds sourceCodeStatement so we can forcefully insert raw source code when not yet available
  • For example, adding C++ code that the parser can't handle
• Adds OKL_MODE macro that is defined as the upper-cased mode (e.g. CUDA -> "CUDA", OpenMP -> "OPENMP")
• Replaces janky expressionStatement + identifierNode hacks with sourceCodeStatement

[codecov]

Codecov Report

Merging #409 into main will decrease coverage by 0.02%.
The diff coverage is 94.47%.

@@            Coverage Diff             @@
##             main     #409      +/-   ##
==========================================
- Coverage   76.36%   76.33%   -0.03%     
==========================================
  Files         239      240       +1     
  Lines       18411    18425      +14     
==========================================
+ Hits        14059    14065       +6     
- Misses       4352     4360       +8     

Impacted Files	Coverage Δ
bin/occa.cpp	38.32% <0.00%> (-0.15%)	⬇️
include/occa/lang/statement/statement.hpp	100.00% <ø> (ø)
src/lang/modes/cuda.cpp	98.43% <ø> (-0.03%)	⬇️
src/lang/modes/metal.cpp	84.94% <ø> (-0.17%)	⬇️
src/lang/modes/opencl.cpp	94.70% <ø> (-0.04%)	⬇️
src/lang/statement/statement.cpp	70.99% <ø> (ø)
src/lang/statement/sourceCodeStatement.cpp	65.00% <65.00%> (ø)
include/occa/lang/utils/array.hpp	100.00% <100.00%> (ø)
src/lang/modes/withLauncher.cpp	96.72% <100.00%> (-0.10%)	⬇️
src/lang/preprocessor.cpp	80.45% <100.00%> (+0.04%)	⬆️
... and 1 more