Implement some minor UX improvements

[Robbepop]

• Implement Default for Store<T> where T: Default.
  • This serves a purpose for a simple Wasmi setup.
• Implement WasmTy for f32 and f64.
  • This allows to use f32 and f64 instead of F32 and F64 for APIs such as func_wrap.
• Enable Config::tail_call and Config::extended_const by default.
  • Those Wasm proposals have been moved to phase 4 for many months now.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 5 lines in your changes are missing coverage. Please review.

Project coverage is 80.82%. Comparing base (26ea8ad) to head (4a9f742).

Files	Patch %	Lines
crates/wasmi/src/store.rs	0.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1031      +/-   ##
==========================================
- Coverage   80.83%   80.82%   -0.01%     
==========================================
  Files         269      269              
  Lines       24803    24806       +3     
==========================================
  Hits        20049    20049              
- Misses       4754     4757       +3     

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