Call `BasicSymbolic` arithmetic operations to construct `similarterm`

[bowenszhu]

resolve https://github.com/JuliaSymbolics/SymbolicUtils.jl/issues/462 resolve https://github.com/JuliaSymbolics/Symbolics.jl/issues/704

In the docstring of similarterm, it says that the return type may be different than t.

https://github.com/JuliaSymbolics/SymbolicUtils.jl/blob/6964c768e76dcbc48ee7b1d58fae481d46caa5a0/src/types.jl#L509-L514

However, the type is directly hard-coded according to f in the code.

https://github.com/JuliaSymbolics/SymbolicUtils.jl/blob/6964c768e76dcbc48ee7b1d58fae481d46caa5a0/src/types.jl#L530-L550

[codecov-commenter]

Codecov Report

Merging #480 (86de974) into master (6964c76) will decrease coverage by 0.50%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #480      +/-   ##
==========================================
- Coverage   82.77%   82.26%   -0.51%     
==========================================
  Files          12       12              
  Lines        1521     1517       -4     
==========================================
- Hits         1259     1248      -11     
- Misses        262      269       +7     

Impacted Files	Coverage Δ
src/types.jl	83.14% <100.00%> (-1.05%)	:arrow_down:
src/polyform.jl	94.36% <0.00%> (-0.38%)	:arrow_down:

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[shashi]

could you review the parts you wrote in #482