Apply shellcheck to all vscodium shell scripts

[zpiatt]

All shell scripts within the VSCodium repository's now pass shellcheck.

1. Fixed glob used in command name ( Unclear functions related to Shellcheck errors #1570 ).
2. Fixed typo causing logical error piping into true ( Unclear functions related to Shellcheck errors #1570 ).
3. Fixed options specified in getopts but not handled by case statement https://www.shellcheck.net/wiki/SC2213
4. Handled invalid flags ( with implied continue ) in case statements ( https://www.shellcheck.net/wiki/SC2220 ).
5. Read error codes directly (style) ( https://www.shellcheck.net/wiki/SC2181 ).
6. Fixed all instances of reading/writing files in same pipeline (https://www.shellcheck.net/wiki/SC2094).
7. Removed legacy back-ticks ( used $( command ) with spaces) (https://www.shellcheck.net/wiki/SC2006).
8. Removed useless cat (https://www.shellcheck.net/wiki/SC2002).
9. Added -r to read commands (https://www.shellcheck.net/wiki/SC2162).

Special shellcheck considerations:

1. shellcheck recommends many style changes for both readability and consistency ( both subjective ). Where applicable I've ignored these messages to conform with the style preference of the project. One example is: https://www.shellcheck.net/wiki/SC2129
2. shellcheck notes when it is unable to follow variables or files when sourced. When applicable, I ignored this message (https://www.shellcheck.net/wiki/SC1091) with a directive (https://github.com/koalaman/shellcheck/wiki/directive).
3. I believe the shellcheck disable messages are a value add, because they cut down on the noise when searching for actual errors.

Other small changes:

1. I standardized all > /dev/null 2>&1 to simply &> /dev/null. I found it both ways and chose the latter.
2. I standardized newlines in if statements and for loops.
3. I standardized all shebangs with #!/usr/bin/env bash.
4. I standardized all tests with [[ ]].

[zpiatt]

I apologize, I made a note and forgot to come back to it. I found the variable PRODUCT_SKU assigned in build/windows/msi/build.sh that doesn't appear to be referenced anywhere else in the project as below:

~/git/vscodium $ grep -rn "PRODUCT_SKU"
build/windows/msi/build.sh:14:  PRODUCT_SKU="vscodium-insiders"
build/windows/msi/build.sh:21:  PRODUCT_SKU="vscodium"

[zpiatt]

I'm not certain the failed check is related to changes I've made. The workflow is attempting to download node.js 16.17.1 linux armv7l but the current LTS Linux ARMv7 is node-v18.17.0-linux-armv7l.tar. It appears the node version is being specified as 16 here: .github/workflows/insider-linux.yml. The link in the log also fails using: https://nodejs.org.

[daiyam]

The variable PRODUCT_SKU can be removed.

I've re-running the failed action because it can failed at that step due to network issue (I think) from time to time...

[zpiatt]

The variable PRODUCT_SKU can be removed.

I've re-running the failed action because it can failed at that step due to network issue (I think) from time to time...

Yes, and I'll remove my erroneous "ignore" as well.

[daiyam]

I've re-running the failed action because it can failed at that step due to network issue (I think) from time to time...

The action have passed.

[zpiatt]

I've re-running the failed action because it can failed at that step due to network issue (I think) from time to time...

The action have passed.

Ok, I've made the other changes. Do you want me to commit them now?

[daiyam]

Ok, I've made the other changes. Do you want me to commit them now?

Yes, you can.

[daiyam]

LGTM!

Thank you for the PR!