Cherry-pick of #80547 for the 6.2 release branch.
---
Explanation: This cherry picks the implementation of SE-0477 to add a
string interpolation method with a `default:` parameter for optional
interpolation values.
Main Branch PR: https://github.com/swiftlang/swift/pull/80547
Risk: Low.
Reviewed By: @stephentyrone
Resolves: rdar://150865613
Testing: New tests for the string interpolations and fix-its.
SE-0329 defines the following static factory methods:
```
public static func seconds<T: BinaryInteger>(_ seconds: T) -> Duration
public static func seconds(_ seconds: Double) -> Duration
public static func milliseconds<T: BinaryInteger>(_ milliseconds: T) -> Duration
public static func milliseconds(_ milliseconds: Double) -> Duration
public static func microseconds<T: BinaryInteger>(_ microseconds: T) -> Duration
public static func microseconds(_ microseconds: Double) -> Duration
public static func nanoseconds<T: BinaryInteger>(_ value: T) -> Duration
```
For no good reason, the obvious additional method:
```
public static func nanoseconds(_ nanoseconds: Double) -> Duration
```
was omitted. After talking this through with the LSG, we have decided
that this is simply a bug, and we will add this method without formal
evolution review.
The empty-arguments test fails when run against an older runtime, so don't test it there.
I tried to do this before, but got the condition backwards.
rdar://146839898
(cherry picked from commit b2f1b44b95)
Print diagnostic groups as part of the LLVM printer in the same manner as the
Swift one does, always. Make `-print-diagnostic-groups` an inert option, since we
always print diagnostic group names with the `[#GroupName]` syntax.
As part of this, we no longer render the diagnostic group name as part
of the diagnostic *text*, instead leaving it up to the diagnostic
renderer to handle the category appropriately. Update all of the tests
that were depending on `-print-diagnostic-groups` putting it into the
text to instead use the `{{documentation-file=<file name>}}`
diagnostic verification syntax.
We've been converging the implementations of educational notes and
diagnostic groups, where both provide category information in
diagnostics (e.g., `[#StrictMemorySafety]`) and corresponding
short-form documentation files. The diagnostic group model is more
useful in a few ways:
* It provides warnings-as-errors control for warnings in the group
* It is easier to associate a diagnostic with a group with
GROUPED_ERROR/GROUPED_WARNING than it is to have a separate diagnostic
ID -> mapping.
* It is easier to see our progress on diagnostic-group coverage
* It provides an easy name to use for diagnostic purposes.
Collapse the educational-notes infrastructure into diagnostic groups,
migrating all of the existing educational notes into new groups.
Simplify the code paths that dealt with multiple educational notes to
have a single, possibly-missing "category documentation URL", which is
how we're treating this.
Explicitly skip `expectCrashLater()` tests for WASI, instead of conditionally excluding them from compilation.
In doing so, restored some tests that were wrongly excluded from the WASI tests suite.
