[JITLink] Switch to SymbolStringPtr for Symbol names (#115796)

Use SymbolStringPtr for Symbol names in LinkGraph. This reduces string interning
on the boundary between JITLink and ORC, and allows p

[JITLink] Switch to SymbolStringPtr for Symbol names (#115796)

Use SymbolStringPtr for Symbol names in LinkGraph. This reduces string interning
on the boundary between JITLink and ORC, and allows pointer comparisons (rather
than string comparisons) between Symbol names. This should improve the
performance and readability of code that bridges between JITLink and ORC (e.g.
ObjectLinkingLayer and ObjectLinkingLayer::Plugins).

To enable use of SymbolStringPtr a std::shared_ptr<SymbolStringPool> is added to
LinkGraph and threaded through to its construction sites in LLVM and Bolt. All
LinkGraphs that are to have symbol names compared by pointer equality must point
to the same SymbolStringPool instance, which in ORC sessions should be the pool
attached to the ExecutionSession.
---------

Co-authored-by: Lang Hames <lhames@gmail.com>

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Reapply [BOLT] DataAggregator support for binaries with multiple text segments (#118023)

When a binary has multiple text segments, the Size is computed as the
difference of the last address of thes

Reapply [BOLT] DataAggregator support for binaries with multiple text segments (#118023)

When a binary has multiple text segments, the Size is computed as the
difference of the last address of these segments from the BaseAddress.
The base addresses of all text segments must be the same.

Introduces flag 'perf-script-events' for testing, which allows passing
perf events without BOLT having to parse them by invoking 'perf script'.
The flag is used to pass a mock perf profile that has two memory
mappings for a mock binary that has two text segments. The mapping
size is updated as `parseMMapEvents` now processes all text segments.

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[BOLT] DataAggregator support for binaries with multiple text segments (#92815)

When a binary has multiple text segments, the Size is computed as the
difference of the last address of these segment

[BOLT] DataAggregator support for binaries with multiple text segments (#92815)

When a binary has multiple text segments, the Size is computed as the
difference of the last address of these segments from the BaseAddress.
The base addresses of all text segments must be the same.

Introduces flag 'perf-script-events' for testing. It allows passing perf events
without BOLT having to parse them using 'perf script'. The flag is used to
pass a mock perf profile that has two memory mappings for a mock binary
that has two text segments. The size of the mapping is updated as this
change `parseMMapEvents` processes all text segments.

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