manuals: replace hyphens with em dashes

Fix some hyphens being improperly used as em dashes.
See https://www.grammarly.com/blog/hyphens-and-dashes/

Using em dashes may also allow Sphinx to hyphenate
and break lines in the best way.

Note that the first character after an em dash not
supposed to be capitalized, unless a specific
rule applies, typically when what follows is a proper noun.

Fix a few misuses of parentheses in following text.

(From yocto-docs rev: a0d93ea1ddfdfbcde8dac3aa328307be778f9e3c)

Signed-off-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Steve Sakoman <steve@sakoman.com>

documentation/kernel-dev/advanced.rst

@@ -182,7 +182,7 @@ the structure:
    order to define a base kernel policy or major kernel type to be
    reused across multiple BSPs, place the file in ``ktypes`` directory.
 
-These distinctions can easily become blurred - especially as out-of-tree
+These distinctions can easily become blurred --- especially as out-of-tree
 features slowly merge upstream over time. Also, remember that how the
 description files are placed is a purely logical organization and has no
 impact on the functionality of the kernel Metadata. There is no impact

documentation/kernel-dev/concepts-appx.rst

@@ -117,7 +117,7 @@ upstream Linux kernel development and are managed by the Yocto Project
 team's Yocto Linux kernel development strategy. It is the Yocto Project
 team's policy to not back-port minor features to the released Yocto
 Linux kernel. They only consider back-porting significant technological
-jumps - and, that is done after a complete gap analysis. The reason
+jumps --- and, that is done after a complete gap analysis. The reason
 for this policy is that back-porting any small to medium sized change
 from an evolving Linux kernel can easily create mismatches,
 incompatibilities and very subtle errors.