Factor out RawFileSystem.

[ericsnowcurrently]

(for #8995)

This separates the low-level filesystem operations from the high-level "fs utils". The move to the VS Code FS API can then happen strictly inside RawFileSystem. Also, this is part of what we reverted in #8970.

Note that the bulk of the changes are in test code. Also, of the non-test code, the changes are either just moving things around (from FileSystem to RawFileSystem), or adding the new RawFileSystem class (and IRawFileSystem interface).

[codecov-io]

Codecov Report

Merging #9499 into master will decrease coverage by 0.6%.
The diff coverage is 57.74%.

@@            Coverage Diff             @@
##           master    #9499      +/-   ##
==========================================
- Coverage   60.79%   60.19%   -0.61%     
==========================================
  Files         551      556       +5     
  Lines       29666    31842    +2176     
  Branches     4486     5138     +652     
==========================================
+ Hits        18036    19167    +1131     
- Misses      10620    11589     +969     
- Partials     1010     1086      +76

Impacted Files	Coverage Δ
src/client/common/platform/types.ts	100% <ø> (ø)	⬆️
src/client/common/platform/fileSystem.ts	58.67% <57.74%> (+32.86%)	⬆️
...ence/interactive-common/intellisense/conversion.ts	30.61% <0%> (-8.52%)	⬇️
src/client/common/terminal/service.ts	86.76% <0%> (-5.97%)	⬇️
src/client/activation/refCountedLanguageServer.ts	34.78% <0%> (-5.22%)	⬇️
src/client/common/terminal/factory.ts	91.3% <0%> (-5.13%)	⬇️
...atascience/interactive-window/interactiveWindow.ts	14.21% <0%> (-4.45%)	⬇️
src/client/common/asyncDisposableRegistry.ts	18.18% <0%> (-4.05%)	⬇️
src/client/sourceMapSupport.ts	78.72% <0%> (-2.13%)	⬇️
src/client/activation/jedi.ts	19.81% <0%> (-2.07%)	⬇️
... and 43 more

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[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!

0 Bugs
0 Vulnerabilities (and 1 Security Hotspot to review)
0 Code Smells

No Coverage information
0.0% Duplication