[CI] Enable Swift format check

[shahmishal]

** Running swift format lint...
Sources/ComplexModule/Complex+AlgebraicField.swift:61:11: warning: [IdentifiersMustBeASCII] remove non-ASCII characters from 'wʹ': ʹ
Sources/ComplexModule/Complex+AlgebraicField.swift:62:11: warning: [IdentifiersMustBeASCII] remove non-ASCII characters from 'zʹ': ʹ
Sources/ComplexModule/Complex+AlgebraicField.swift:114:9: warning: [IdentifiersMustBeASCII] remove non-ASCII characters from 'wʹ': ʹ
Sources/ComplexModule/Complex+AlgebraicField.swift:115:9: warning: [IdentifiersMustBeASCII] remove non-ASCII characters from 'zʹ': ʹ
Sources/ComplexModule/Complex+ElementaryFunctions.swift:238:9: warning: [IdentifiersMustBeASCII] remove non-ASCII characters from 'θ': θ
Sources/ComplexModule/Complex+ElementaryFunctions.swift:341:9: warning: [IdentifiersMustBeASCII] remove non-ASCII characters from 'θ': θ
Sources/ComplexModule/Complex+ElementaryFunctions.swift:358:9: warning: [IdentifiersMustBeASCII] remove non-ASCII characters from 'y²': ²
Sources/_TestSupport/DoubleWidth.swift:305:9: warning: [AlwaysUseLowerCamelCase] rename the constant 'quotient_' using lowerCamelCase
Sources/_TestSupport/DoubleWidth.swift:311:9: warning: [AlwaysUseLowerCamelCase] rename the constant 'remainder_' using lowerCamelCase
Sources/_TestSupport/DoubleWidth.swift:395:9: warning: [AlwaysUseLowerCamelCase] rename the constant 'quotient_' using lowerCamelCase
Sources/_TestSupport/DoubleWidth.swift:401:9: warning: [AlwaysUseLowerCamelCase] rename the constant 'remainder_' using lowerCamelCase
Sources/_TestSupport/DoubleWidth.swift:666:11: warning: [AlwaysUseLowerCamelCase] rename the constant 'lhs_' using lowerCamelCase
Tests/IntegerUtilitiesTests/DoubleWidthTests.swift:420:8: warning: [AlwaysUseLowerCamelCase] rename the function 'testConversions_ToAndFromString' using lowerCamelCase

[stephentyrone]

I think we want to simply turn off IdentifiersMustBeASCII here, and fix up the others.