Apply clangd IWYU export pragmas to transitive includes

[eramongodb]

To improve the quality of clangd's IWYU diagnostics, this PR applies the IWYU "export" macro to deliberate transitive includes.

Include directives which are "exported" are:

• publically documented transitive includes (with \par Includes), or
• include of a direct component header (forward, declaration, internal, or test).

All clangd IWYU warnings in v1 components (or required by v1 components) are addressed. Reordering or removal of includes in v_noabi public headers are skipped to avoid unnecessary potential for breaking changes.

Even with these changes, the IWYU tool still emits noise, e.g. <bsoncxx/private/bson.hh> exports <bson/bson.h>, but some components still emit the following warnings:

No header providing "bson_t" is directly included (fix available) [clangd(missing-includes)]
No header providing "bson_malloc" is directly included (fix available) [clangd(missing-includes)]
No header providing "BSON_VERSION_S" is directly included (fix available) [clangd(missing-includes)]
...

despite other entities provided by <bson/bson.h> being (correctly) handled by the export. The <bson/bson.h> might need to be annotated with similar comments for these warnings to go away. Similarly, <type_traits> does not seem to be identified via <bsoncxx/private/type_traits.hh> -> <bsoncxx/v1/detail/type_traits.hpp> -> <type_traits> either. (Possibly related: include-what-you-use/include-what-you-use#1645)

Update: confirmed these are due to the lack of IWYU export pragmas in <bson/bson.h>: mongodb/mongo-c-driver#2167.

Fixing warnings for missing IWYU of third party library headers (e.g. Catch2 and <catch2/catch_message.hpp>) are skipped by this PR. Unsure if there is a nice way to silence these warnings for headers we do not own. The following can be added to the clangd configuration file (either per-project or global):

Diagnostics:
  Includes:
    IgnoreHeader: .*/_deps/.*