enh(directx): Add do-while loop support to DirectX backend

[MashyBasker]

PR Description

Implementation details:

• Added "DO" token in lexer.
• Implemented DoWhileNode in DirectxAst.py to create do-while node in the AST
• Added logic to parse do-while statement when "DO" token is read
• Implemented do-while code generation from CrossGL

Test details:

• Added parser test for do-while
• Added code generation test for do-while

Related Issue

Fixes #192

shader Sample

shader main {
    struct VSInput {
        vec4 position @ POSITION;
        vec4 color @ TEXCOORD0;
    }
    struct VSOutput {
        vec4 out_position @ TEXCOORD0;
    }
    struct PSInput {
        vec4 in_position @ TEXCOORD0;
    }
    struct PSOutput {
        vec4 out_color @ gl_FragColor0;
    }
    // Vertex Shader
    vertex {
       VSOutput VSMain(VSInput input )  {
        VSOutput output;
        output.out_position = input.position;
        int i = 0;
        do {
            output.out_position = input.color;
            i =  i + 1;
        } while ( i < 10);
        return  output;
    }

    }

    // Fragment Shader
    fragment {
       PSOutput PSMain(PSInput input )  {
        PSOutput output;
        output.out_color = input.in_position;
        int i = 0;
        do {
            output.out_color = vec4(1.0, 1.0, 1.0, 1.0);
            i =  i + 1;
        } while ( i < 10);
        return  output;
    }

    }

}

The above CrossGL code was generated from the following DirectX code:

struct VSInput {
        float4 position : POSITION;
        float4 color : TEXCOORD0;
    };
    struct VSOutput {
        float4 out_position : TEXCOORD0;
    };
    VSOutput VSMain(VSInput input) {
        VSOutput output;
        output.out_position = input.position;
        int i = 0;
        do {
            output.out_position = input.color;
            i = i + 1;  // Increment the loop variable
        } while (i < 10);
        return output;
    }
    struct PSInput {
        float4 in_position : TEXCOORD0;
    };
    struct PSOutput {
        float4 out_color : SV_TARGET0;
    };
    PSOutput PSMain(PSInput input) {
        PSOutput output;
        output.out_color = input.in_position;
        int i = 0;
        do {
            output.out_color = float4(1.0, 1.0, 1.0, 1.0);
            i = i + 1;  // Increment the loop variable
        } while (i < 10);
        return output;
    }

Checklist

• Have you added the necessary tests?
• Only modified the files mentioned in the related issue(s)?
• Are all tests passing?

[samthakur587]

LGTM 🚀
great work @MashyBasker thanks for contributing here.