Parse pragma solidity version numbers

[seanyoung]

Many Solidity features depend on the version of the compiler. So, parse the version pragma and in another PR we will use this information.

This PR adds pragmas to the ast and we test it with a graphviz dot file.

[codecov[bot]]

Codecov Report

Attention: 70 lines in your changes are missing coverage. Please review.

Comparison is base (221ecd1) 87.65% compared to head (38ec432) 87.90%. Report is 1 commits behind head on main.

Files	Patch %	Lines
solang-parser/src/helpers/fmt.rs	20.83%	38 Missing :warning:
src/sema/dotgraphviz.rs	82.79%	16 Missing :warning:
solang-parser/src/pt.rs	0.00%	6 Missing :warning:
src/bin/doc/mod.rs	0.00%	3 Missing :warning:
src/sema/ast.rs	88.88%	3 Missing :warning:
src/codegen/cfg.rs	0.00%	1 Missing :warning:
src/sema/expression/function_call.rs	98.33%	1 Missing :warning:
src/sema/expression/member_access.rs	90.00%	1 Missing :warning:
src/sema/mod.rs	98.93%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1593 +/- ## ========================================== + Coverage 87.65% 87.90% +0.24% ========================================== Files 133 133 Lines 64300 64620 +320 ========================================== + Hits 56363 56803 +440 + Misses 7937 7817 -120 ```

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[seanyoung]

@LucasSte @xermicus let me know if you're interested in reviewing this, else I will merge it

[LucasSte]

@LucasSte @xermicus let me know if you're interested in reviewing this, else I will merge it

I'm reviewing it.