[lldb] Update Swift String summary formatter for new bridged case

[kastiglione]

Supports a new discriminator case: "immortal, bridged". Added in swiftlang/swift#74881.

There are now three bridged cases: immortal, shared, foreign. The top 4 bits of the discriminator of these cases are:

Case	Bits
immortal	1100
shared	0100
foreign	0101

This change updates the mask used to recognize immortal bridged strings. Previously the mask was 0b1110, which checked the top bit (for zero). Now the mask is 0b0110, which ignores the top bit. When the middle two bits are 10, then it's treated as a bridged string.

rdar://141019389

[kastiglione]

Working on a test, putting this up for initial feedback in the meantime.

[Catfish-Man]

Thanks for doing this! It looks correct to me: the second bit of the discriminator indicates "is bridged", but overloaded to mean something else if the third bit is 1.

[kastiglione]

@swift-ci test

[adrian-prantl]

@swift-ci test windows