Add LogSoftmax and LogSigmoid support

[lrw04]

The patch adds LogSoftmax and LogSigmoid layers to ncnn and respective passes to pnnx.

[tencent-adm]

All committers have signed the CLA.

[codecov-commenter]

Codecov Report

Merging #4921 (51ccd56) into master (0a8cf31) will increase coverage by 0.00%.
Report is 1 commits behind head on master.
The diff coverage is 95.53%.

@@           Coverage Diff            @@
##           master    #4921    +/-   ##
========================================
  Coverage   94.91%   94.91%            
========================================
  Files         776      778     +2     
  Lines      226096   226275   +179     
========================================
+ Hits       214589   214760   +171     
- Misses      11507    11515     +8     

Files Changed	Coverage Δ
src/layer/logsoftmax.cpp	95.00% <95.00%> (ø)
src/layer/logsigmoid.cpp	100.00% <100.00%> (ø)

[lrw04]

Wait, is it better to rewrite logsigmoid/logsoftmax nodes into a log node and a sigmoid/softmax node in pnnx's pass_ncnn? This helps removing duplicate code but achieving higher numerical stability is impossible with this solution.

[nihui]

Wait, is it better to rewrite logsigmoid/logsoftmax nodes into a log node and a sigmoid/softmax node in pnnx's pass_ncnn? This helps removing duplicate code but achieving higher numerical stability is impossible with this solution.

For code reuse, additional parameters can be added to the existing sigmoid/softmax
In this way, there is no need to add additional layer types

[lrw04]

Is it better to rewrite logxxx nodes into a log node + a xxx node? I will submit another PR soon.