everywhere: replace double words

[JordanYates]

Treewide search and replace on a range of double word combinations:
* the the
* to to
* if if
* that that
* on on
* is is
* from from

Add double prepositions to the default spelling check list.

[LingaoM]

Learn by analogy: there are also to to, that that, for for, etc...

[LingaoM]

to to, if if, that that, on on, is is
So I recommend filtering all words.

[kartben]

I'm with @LingaoM , let's do even more if you don't mind, @JordanYates :)

You may also want to search more smartly, something like the\n\s+(?:\* )?the will give you things like:

• zephyr/drivers/sensor/st/lis2dh/Kconfig

  Lines 158 to 160 in 7f0f0a4

  	to the result. The offset can be obtained by comparing the
  	the reported temperature to a reference.
  	This option does not apply to the LSM330DLHC.

• zephyr/include/zephyr/crypto/crypto.h

  Lines 476 to 478 in 7f0f0a4

  	* This function can be called zero or more times, passing a slice of the
  	* the data. The hash is calculated using all the given pieces.
  	* To calculate the hash call @c hash_compute().

[aescolar]

to to, if if, that that, on on, is is

@LingaoM Please note that a PR should not be blocked to demand "more" fixes (https://docs.zephyrproject.org/latest/contribute/contributor_expectations.html#reviewer-expectations9.
If @JordanYates is kind enough to take it further that would be certainly very nice of him.
But this PR is improving something, and we cannot demand from contributors they spend their time fixing even more things just because we realize about them.

[kartben]

cool cool ❤️

[nashif]

hopefully this did not remove any valid wink wink occurances :-D

[Thalley]

Would it make sense to add this sort of check to CI?

[JordanYates]

Would it make sense to add this sort of check to CI?

This PR includes an update to spelling.txt to try and catch these in the future.
It's not smart enough to catch a repetition across lines, but its what we have.