docs: replace `FOO by :term:FOO` where possible

If a variable has a glossary entry and some rST files write about those
variables, it's better to point to the glossary entry instead of just
highlighting it by surrounding it with two tick quotes.

This was automated by the following python script:
"""
import re
from pathlib import Path

with open('objects.inv.txt', 'r') as f:
    objects = f.readlines()

with open('bitbake-objects.inv.txt', 'r') as f:
    objects = objects + f.readlines()

re_term = re.compile(r'variables.html#term-([A-Z_0-9]*)')
terms = []

for obj in objects:
    match = re_term.search(obj)
    if match and match.group(1):
        terms.append(match.group(1))

for rst in Path('.').rglob('*.rst'):
    with open(rst, 'r') as f:
        content = "".joing(f.readlines())
    for term in terms:
        content = re.sub(r'``({})``(?!.*\s*[~-]+)'.format(term), r':term:`\1`', content)

    with open(rst, 'w') as f:
        f.write(content)
"""

(From yocto-docs rev: ba49d9babfcb84bc5c26a68c8c3880a1d9c236d3)

Signed-off-by: Quentin Schulz <foss@0leil.net>
Reviewed-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
Reviewed-by: Nicolas Dechesne <nicolas.dechesne@linaro.org>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/ref-manual/terms.rst

@@ -97,11 +97,11 @@ universal, the list includes them just in case:
       .. note::
 
          By default, the Build Directory contains :term:`TMPDIR`, which is a
-         temporary directory the build system uses for its work. ``TMPDIR`` cannot
+         temporary directory the build system uses for its work. :term:`TMPDIR` cannot
          be under NFS. Thus, by default, the Build Directory cannot be under
          NFS. However, if you need the Build Directory to be under NFS, you can
-         set this up by setting ``TMPDIR`` in your ``local.conf`` file to use a local
-         drive. Doing so effectively separates ``TMPDIR`` from :term:`TOPDIR`, which is the
+         set this up by setting :term:`TMPDIR` in your ``local.conf`` file to use a local
+         drive. Doing so effectively separates :term:`TMPDIR` from :term:`TOPDIR`, which is the
          Build Directory.
 
    :term:`Build Host`