Add option to prevent code for external live bindings

[lukastaegert]

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

List any relevant issue numbers:

Description

This adds an option to prevent additional code that is generated to support live bindings with external dependencies. At the moment, three situations will be affected by this option:

// reexporting an external value
export {x} from 'external';

// reexporting an external namespace
export * from 'external';

// dynamically importing an external dependency
import('external').then(...)

This will eliminate most situations where Rollup uses getters and makes the code more efficient at the cost of spec compliancy. Circular dependencies involving external dependencies may not longer work if this option is used.

The remaining situations where Rollup will generate getters in the code that are not touched by this option are:

• reexports from chunks that mutate their exports Example
• accessing a reified dynamic namespace before the module was run when there are circular dependencies Example

[codecov]

Codecov Report

Merging #3010 into master will increase coverage by 0.06%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #3010      +/-   ##
==========================================
+ Coverage    87.8%   87.86%   +0.06%     
==========================================
  Files         166      166              
  Lines        5641     5647       +6     
  Branches     1720     1722       +2     
==========================================
+ Hits         4953     4962       +9     
  Misses        412      412              
+ Partials      276      273       -3

Impacted Files	Coverage Δ
src/utils/mergeOptions.ts	88.09% <ø> (ø)	⬆️
src/finalisers/shared/getInteropNamespace.ts	100% <100%> (ø)	⬆️
src/finalisers/shared/getExportBlock.ts	87.71% <100%> (+0.44%)	⬆️
src/finalisers/amd.ts	94.28% <100%> (ø)	⬆️
src/finalisers/cjs.ts	94.87% <100%> (ø)	⬆️
src/Chunk.ts	91.2% <100%> (+0.01%)	⬆️
src/ast/nodes/Import.ts	100% <0%> (+6.81%)	⬆️

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