🍒 [5.6] backtrack on part of SE-327 dealing with default-value exprs

[kavon]

This effectively reverts 6823744

The blanket removal of isolation in default-value expressions had
unintented consequences for important workflows. It's still
a problem that needs to be addressed, but we need to be more precise
about the problematic situations.

resolves rdar://90665119

[kavon]

@swift-ci please test

[kavon]

The macOS failure is a random CI machine issue.

Windows failure is probably unrelated, but I need to dig in to see why it broke. A cursory look suggests a change in the number of expected diagnostics, which could be due to the removal of warnings from this PR:

Input file: <stdin>

Check file: C:\Users\swift-ci\jenkins\workspace\swift-PR-windows\swift\test\ModuleInterface\ModuleCache\module-cache-diagnostics.swift



-dump-input=help explains the following input dump.



Input was:

<<<<<<

            1: BUILD_DIR\test-windows-x86_64\ModuleInterface\ModuleCache\Output\module-cache-diagnostics.swift.tmp\LeafModule.swiftinterface:7:8: error: no such module 'NotAModule' [] [] 

            2: Number FIXITs = 0 

            3: BUILD_DIR\test-windows-x86_64\ModuleInterface\ModuleCache\Output\module-cache-diagnostics.swift.tmp\OtherModule.swiftinterface:4:8: error: failed to build module 'LeafModule' for importation due to the errors above; the textual interface may be broken by project issues or a compiler bug [] [] 

check:61'0                                                                                                                                                                                                                                                                                                    X~~~~~~ error: no match found

            4: Number FIXITs = 0 

check:61'0     ~~~~~~~~~~~~~~~~~~

            5: BUILD_DIR\test-windows-x86_64\ModuleInterface\ModuleCache\Output\module-cache-diagnostics.swift.tmp\LeafModule.swiftinterface:98:8: error: failed to build module 'OtherModule' for importation due to the errors above; the textual interface may be broken by project issues or a compiler bug [] [] 

check:61'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

check:61'1                                                                                             ?                                                                                                                                                                                                               possible intended match

            6: Number FIXITs = 0 

check:61'0     ~~~~~~~~~~~~~~~~~~

            7: Number of diagnostics: 3 

check:61'0     ~~~~~~~~~~~~~~~~~~~~~~~~~

>>>>>>


error: command failed with exit status: 1

[kavon]

@swift-ci please test Windows

[kavon]

@swift-ci please test macOS