Fix "default" reexport issues in non ESM/System formats

[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:
Resolves #2992
Resolves #2977

Description

This fixes two very important issues that could lead to incorrect code in all formats except ESM and System when a default export of an external dependency is reexported.

This is the first:
https://rollupjs.org/repl/?version=1.20.2&shareable=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

Note how in line 7, a non-existing variable foo_default is accessed.

This is the second:
https://rollupjs.org/repl/?version=1.20.2&shareable=JTdCJTIybW9kdWxlcyUyMiUzQSU1QiU3QiUyMm5hbWUlMjIlM0ElMjJtYWluLmpzJTIyJTJDJTIyY29kZSUyMiUzQSUyMmV4cG9ydCUyMCU3QiUyMGRlZmF1bHQlMjAlN0QlMjBmcm9tJTIwJTVDJTIyZXh0ZXJuYWwlNUMlMjIlM0IlMjIlMkMlMjJpc0VudHJ5JTIyJTNBdHJ1ZSU3RCU1RCUyQyUyMm9wdGlvbnMlMjIlM0ElN0IlMjJmb3JtYXQlMjIlM0ElMjJhbWQlMjIlMkMlMjJuYW1lJTIyJTNBJTIybXlCdW5kbGUlMjIlMkMlMjJhbWQlMjIlM0ElN0IlMjJpZCUyMiUzQSUyMiUyMiU3RCUyQyUyMmdsb2JhbHMlMjIlM0ElN0IlN0QlN0QlMkMlMjJleGFtcGxlJTIyJTNBbnVsbCU3RA==

Not how first in the interop block, the default is assigned to the "external" variable and then later, the export is taken from external.default and not external.

[codecov]

Codecov Report

Merging #3084 into master will increase coverage by 0.13%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #3084      +/-   ##
==========================================
+ Coverage   88.81%   88.95%   +0.13%     
==========================================
  Files         165      165              
  Lines        5731     5721      -10     
  Branches     1743     1741       -2     
==========================================
- Hits         5090     5089       -1     
+ Misses        388      385       -3     
+ Partials      253      247       -6

Impacted Files	Coverage Δ
src/finalisers/shared/getExportBlock.ts	100% <100%> (+12.28%)	⬆️
src/finalisers/shared/getInteropBlock.ts	100% <100%> (+18.18%)	⬆️

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