Refactor: seperate rendering context

[chenshenhai]

• feat: add toDataURL to idraw
• feat: add helperContext to @idraw/board
• refactor: add Context render to @idraw/renderer
• refactor: rename getDisplayContext2D and getOriginContext2D

[codecov-commenter]

Codecov Report

Merging #118 (3ddd6a2) into main (947c636) will decrease coverage by 6.16%.
The diff coverage is 63.49%.

@@            Coverage Diff             @@
##             main     #118      +/-   ##
==========================================
- Coverage   30.97%   24.81%   -6.17%     
==========================================
  Files          88       87       -1     
  Lines        3209     3180      -29     
  Branches      709      704       -5     
==========================================
- Hits          994      789     -205     
- Misses       1650     1779     +129     
- Partials      565      612      +47     

Flag	Coverage Δ
unittests	24.81% <63.49%> (-6.17%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
packages/idraw/src/index.ts	56.75% <0.00%> (-1.58%)	⬇️
packages/idraw/src/mixins/file.ts	0.00% <0.00%> (ø)
packages/renderer/src/index.ts	0.00% <0.00%> (ø)
packages/util/src/lib/context.ts	80.82% <0.00%> (+80.82%)	⬆️
packages/board/src/index.ts	60.86% <86.95%> (+2.33%)	⬆️
packages/core/src/index.ts	71.26% <94.44%> (+5.51%)	⬆️
packages/board/src/lib/temp.ts	66.66% <100.00%> (+4.16%)	⬆️
packages/board/src/names.ts	100.00% <100.00%> (ø)
packages/core/src/lib/draw/rect.ts	0.00% <0.00%> (-100.00%)	⬇️
packages/core/src/lib/draw/base.ts	1.47% <0.00%> (-82.36%)	⬇️
... and 11 more

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