build: Generate pkg-config file

So that meson projects can find gi-docgen using dependency function.
3 jobs for pkg-config in 1 minute and 45 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Check
passed #1219001
flake8

00:01:33

failed #1219002
allowed to fail
mypy

00:01:44

passed #1219003
reuse

00:01:45

 
Name Stage Failure
failed
mypy Check
gidocgen/gir/parser.py:925: error: Argument "get_type" to "GType" has incompatible type "Optional[str]"; expected "str"
gidocgen/gir/parser.py:968: error: Argument "get_type" to "GType" has incompatible type "Optional[str]"; expected "str"
gidocgen/gir/parser.py:990: error: Argument "name" to "Union" has incompatible type "Optional[str]"; expected "str"
gidocgen/gir/parser.py:990: error: Argument "symbol_prefix" to "Union" has incompatible type "Optional[str]"; expected "str"
gidocgen/gir/parser.py:990: error: Argument "ctype" to "Union" has incompatible type "Optional[str]"; expected "str"
gidocgen/utils.py:767: error: Need type annotation for 'found_programs' (hint: "found_programs: Dict[<type>, <type>] = ...")
Found 186 errors in 4 files (checked 17 source files)
Cleaning up file based variables
ERROR: Job failed: exit code 1