WASM: Add support for f32 and f64

towards #700

Highlights:

For f32 and f64, it supports

• basic arithmetic operations: add, sub, mul, div
• unary_minus (and thus negative floats)
• constants/literals
• functions and function calls

Testing:

• The generated wasm is converted (converts successfully) to wat using wasm2wat (part of wabt tool) and tested on https://webassembly.github.io/wabt/demo/wat2wasm/ with the following JavaScript code.
• The generated wat is tested on https://webassembly.github.io/wabt/demo/wat2wasm/ with the following (same code as previous) JavaScript code.

Appendix:

Testing Code: WASM: Add float f32 and f64 test case

JavaScript code for executing on https://webassembly.github.io/wabt/demo/wat2wasm/

const wasmInstance =
      new WebAssembly.Instance(wasmModule, {});
const { a_sqr, get_neg_f32, add_floats, get_pi, get_pi_64, z_computecirclearea } = wasmInstance.exports;

console.log(add_floats(2.3, -5.6));
console.log(get_pi())
console.log(get_pi_64())
console.log(z_computecirclearea(5.0))
console.log(get_neg_f32())