startswith/endswith wrap starts_with/ends_with and will eventually go away (to more closely match string_view)

Note that llvm::support::endianness has been renamed to
llvm::endianness while becoming an enum class as opposed to an
enum. This patch replaces support::{big,little,native} with
llvm::endianness::{big,little,native}.

In preparation for removing the `#include "llvm/ADT/StringExtras.h"`
from the header to source file of `llvm/Support/Error.h`, first add in
all the missing includes that were previously included transitively
through this header.

This patch migrates uses of StringRef::{starts,ends}with_insensitive
to StringRef::{starts,ends}_with_insensitive so that we can use names
similar to those used in std::string_view.  I'm planning to deprecate
StringRef::{starts,ends}with_insensitive once the migration is
complete across the code base.

Differential Revision: https://reviews.llvm.org/D150426

This patch replaces the uses of PointerUnion.is function by llvm::isa,
PointerUnion.get function by llvm::cast, and PointerUnion.dyn_cast by
llvm::dyn_cast_if_present. This is according to the FIXME in
the definition of the class PointerUnion.

This patch does not remove them as they are being used in other
subprojects.

Reviewed By: mehdi_amini

Differential Revision: https://reviews.llvm.org/D148449

This reverts commit cfb4e782520ce59602a34732386ebbdf58136cfb.

This reverts commit a3b7cb015fd5fd2aa98afda8ae22759576ce2888.

symbol-offset.test fails under MSAN:

[  1] ; RUN: llvm-pdbutil yaml2pdb %p/Inputs/symbol-offset.yaml --pdb=%t.pdb [FAIL]
llvm-pdbutil yaml2pdb <REDACTED>/llvm/test/tools/llvm-pdbutil/Inputs/symbol-offset.yaml --pdb=<REDACTED>/tmp/symbol-offset.test/symbol-offset.test.tmp.pdb
==9283==WARNING: MemorySanitizer: use-of-uninitialized-value
    #0 0x55f975e5eb91 in __libcpp_tls_set <REDACTED>/include/c++/v1/__threading_support:428:12
    #1 0x55f975e5eb91 in set_pointer <REDACTED>/include/c++/v1/thread:196:5
    #2 0x55f975e5eb91 in void* std::__msan::__thread_proxy<std::__msan::tuple<std::__msan::unique_ptr<std::__msan::__thread_struct, std::__msan::default_delete<std::__msan::__thread_struct> >, llvm::parallel::detail::(anonymous namespace)::ThreadPoolExecutor::ThreadPoolExecutor(llvm::ThreadPoolStrategy)::'lambda'()::operator()() const::'lambda'()> >(void*) <REDACTED>/include/c++/v1/thread:285:27
    #3 0x7f74a1e55b54 in start_thread (<REDACTED>/libpthread.so.0+0xbb54) (BuildId: 64752de50ebd1a108f4b3f8d0d7e1a13)
    #4 0x7f74a1dc9f7e in clone (<REDACTED>/libc.so.6+0x13cf7e) (BuildId: 7cfed7708e5ab7fcb286b373de21ee76)

Right now, if we want to dump symbol at specified offset, we need to use `grep`.
And it can only show surrounding symbols in layout (not in lexical scope sense).

This adds similar options to `dump` command as `llvm-dwarfdump` to allow users
to dump symbol record at specified offset and its parents or children with
spcified depth.

`--symbol-offset=` must be used with `--modi` to dump only one symbol at given
offset.

`--show-parents`/`--show-children` must be used with `--symbol-offset` to
dump all symbols that are parents/children of the symbol at given offset.

`--parent-recurse-depth`/`--children-recurse-depth` must be used with
`--show-parents`/`--show-children` to specify the max up/down depth.

Reviewed By: rnk

Differential Revision: https://reviews.llvm.org/D124317

The change described by:

https://reviews.llvm.org/D122226

Moved some llvm-pdbutil functionality to the debug PDB library.

This patch addresses a broken '-modi' argument handling, which
causes an assertion if its value is other than '0' or '1'.

In addition, it moves the assertion for the number of occurrences
of the '-modi' argument from the PDB library into the llvm-pdbutil
driver.

Reviewed By: zequanwu

Differential Revision: https://reviews.llvm.org/D123483